Lately there's been a lot of hype about the command changes for 1.13 and even more excitement about the new textures. But will 1.13 change anything else, don't get me wrong, what it's already doing is quite momentous but will they add anything new, mobs? Blocks? Features?
They will change all block IDs and the save format, probably breaking every single map viewer and editor until they can be updated. For example, wool will have 16 block IDs instead of one ID and a data value to determine the color, so at the very least every color other than white will need a new ID, and within the save file each chunk section (a 16x16x16 cube) will have a lookup table which translates local numerical IDs (still used by the save format for efficiency purposes) to in-game IDs, with up to 4096 IDs per chunk section (which is also the maximum number of blocks each chunk section can store so this will not be a limitation) and unlimited overall (well, probably the 32 bit integer limit, which is over 2 billion; more practically, limited by memory usage and decreased garbage collector efficiency with large amounts of memory allocated).
Previously, they mostly added support for 4096 block IDs all the way back in 1.2 but due to the fact that item IDs started at 256 and were treated the same as block IDs in many parts of the code this effectively limited the game to 256 block IDs unless you patched in a work-around, such as shifting all item IDs up by 4096 instead of 256 (aside from backwards compatibility with older worlds I don't see any reason why 1.8 should still be affected since they removed numerical IDs, and they could have added a converter for older worlds, which have to be converted anyway due to changes to IDs).
Personally, I don't see vanilla using 4096 block IDs anytime soon and with better usage of data values and/or tile entities you can currently have as many as 65536 different blocks (e.g. Shulker boxes, which are already tile entities, could have used tile entity data to store their color, even allowing for up to 16777216 different colors with commands, for just one block ID; Pocket Edition uses a single block ID with data values for different types of wooden fences instead of one ID per type).
The textures won't be in 1.13, at least according to this tweet by JAPPA. I don't think they're doing much else except for bugfixes and some optimizations (some people already seem to have better FPS in the 1.13 snapshots).
They will change all block IDs and the save format, probably breaking every single map viewer and editor until they can be updated. For example, wool will have 16 block IDs instead of one ID and a data value to determine the color, so at the very least every color other than white will need a new ID, and within the save file each chunk section (a 16x16x16 cube) will have a lookup table which translates local numerical IDs (still used by the save format for efficiency purposes) to in-game IDs, with up to 4096 IDs per chunk section (which is also the maximum number of blocks each chunk section can store so this will not be a limitation) and unlimited overall (well, probably the 32 bit integer limit, which is over 2 billion; more practically, limited by memory usage and decreased garbage collector efficiency with large amounts of memory allocated).
Previously, they mostly added support for 4096 block IDs all the way back in 1.2 but due to the fact that item IDs started at 256 and were treated the same as block IDs in many parts of the code this effectively limited the game to 256 block IDs unless you patched in a work-around, such as shifting all item IDs up by 4096 instead of 256 (aside from backwards compatibility with older worlds I don't see any reason why 1.8 should still be affected since they removed numerical IDs, and they could have added a converter for older worlds, which have to be converted anyway due to changes to IDs).
Personally, I don't see vanilla using 4096 block IDs anytime soon and with better usage of data values and/or tile entities you can currently have as many as 65536 different blocks (e.g. Shulker boxes, which are already tile entities, could have used tile entity data to store their color, even allowing for up to 16777216 different colors with commands, for just one block ID; Pocket Edition uses a single block ID with data values for different types of wooden fences instead of one ID per type).
Changes to commands do not necessarily mean that they will change the actual inner mechanics of how blocks are handled and the save format; commands only mean that you must update commands and command blocks while changes to block IDs themselves means that you will have to convert your worlds, or worst case, start a new world (I doubt they won't include a converter). For example, 1.12 still internally uses the same numerical IDs that have been used since the blocks that used them existed (stone = 1, grass = 2, dirt = 3, etc); if you downgrade only new blocks (items, entities, NBT data) will disappear, while if you downgrade a 1.13+ world it will turn into a jumbled mess of random blocks (at best) and be destroyed beyond all possible repair (because of this very real danger they should do what they did in 1.2 when the game converted to the Anvil format; the first time you loaded an old world the game converted the entire world all at once and new files were created instead of converting chunks on-the-fly as they are loaded. Since the game kept the older files it was even easy to revert back).
See this comment on Reddit for a detailed description of what they will do:
Lately there's been a lot of hype about the command changes for 1.13 and even more excitement about the new textures. But will 1.13 change anything else, don't get me wrong, what it's already doing is quite momentous but will they add anything new, mobs? Blocks? Features?
Just curious, that's all.
They will change all block IDs and the save format, probably breaking every single map viewer and editor until they can be updated. For example, wool will have 16 block IDs instead of one ID and a data value to determine the color, so at the very least every color other than white will need a new ID, and within the save file each chunk section (a 16x16x16 cube) will have a lookup table which translates local numerical IDs (still used by the save format for efficiency purposes) to in-game IDs, with up to 4096 IDs per chunk section (which is also the maximum number of blocks each chunk section can store so this will not be a limitation) and unlimited overall (well, probably the 32 bit integer limit, which is over 2 billion; more practically, limited by memory usage and decreased garbage collector efficiency with large amounts of memory allocated).
Previously, they mostly added support for 4096 block IDs all the way back in 1.2 but due to the fact that item IDs started at 256 and were treated the same as block IDs in many parts of the code this effectively limited the game to 256 block IDs unless you patched in a work-around, such as shifting all item IDs up by 4096 instead of 256 (aside from backwards compatibility with older worlds I don't see any reason why 1.8 should still be affected since they removed numerical IDs, and they could have added a converter for older worlds, which have to be converted anyway due to changes to IDs).
Personally, I don't see vanilla using 4096 block IDs anytime soon and with better usage of data values and/or tile entities you can currently have as many as 65536 different blocks (e.g. Shulker boxes, which are already tile entities, could have used tile entity data to store their color, even allowing for up to 16777216 different colors with commands, for just one block ID; Pocket Edition uses a single block ID with data values for different types of wooden fences instead of one ID per type).
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?
The textures won't be in 1.13, at least according to this tweet by JAPPA. I don't think they're doing much else except for bugfixes and some optimizations (some people already seem to have better FPS in the 1.13 snapshots).
That all falls under what I said about commands.
Just curious, that's all.
Changes to commands do not necessarily mean that they will change the actual inner mechanics of how blocks are handled and the save format; commands only mean that you must update commands and command blocks while changes to block IDs themselves means that you will have to convert your worlds, or worst case, start a new world (I doubt they won't include a converter). For example, 1.12 still internally uses the same numerical IDs that have been used since the blocks that used them existed (stone = 1, grass = 2, dirt = 3, etc); if you downgrade only new blocks (items, entities, NBT data) will disappear, while if you downgrade a 1.13+ world it will turn into a jumbled mess of random blocks (at best) and be destroyed beyond all possible repair (because of this very real danger they should do what they did in 1.2 when the game converted to the Anvil format; the first time you loaded an old world the game converted the entire world all at once and new files were created instead of converting chunks on-the-fly as they are loaded. Since the game kept the older files it was even easy to revert back).
See this comment on Reddit for a detailed description of what they will do:
https://www.reddit.com/r/minecraftsuggestions/comments/6frxfb/meta_can_113_remove_the_block_limit_entirely/diknnwt/
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?