I initially thought this would be just another backpack suggestion- however, the idea of completely revamping the inventory is actually kind of appealing. I too think 27 slots is pretty overpowered early in the game. However, I really don't think Mojang would consider such an idea, if only because of how difficult it would be to balance.
-I like the idea itself. It would make sense that you start with less inventory space. That is, initially you just have the hotbar and no inventory slots. There could be four levels of pack, (leather, iron, gold, diamond, and netherite). Leather gives you one row of inventory, iron gives you two, gold gives one but can be enchanted with various special abilities to give them more space/better stack height/better hotbar size, diamond gives the default inventory, and netherite gives slightly larger than default. Backpacks, like Elytra, would take the place of a regular chestplate, forcing players to prioritize further.
-All in all, I love the idea itself, but I think the odds of such a fundamental system ever being changed are pretty slim. Maybe as a modding request, but I really just can't see this in the base game.
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For me the blast furnace feels like its a bit of a useless feature. One there is not a lot of ores that can be used with it.
Two unless you have a large need for tons of iron or have a large scale iron farm then you probably not even bother using it.
Three the food furnace is a lot better then the blast furnance since there is a lot of foods that can be cooked with it.
Four why would I replace the original furnace that has been in most editions of minecraft when it works decently fine.
I'd like to see the blast furnace setup to handle stone type blocks instead. Why because you have a variety of stone you can work with.
There is nether brick, stone, cut stone, smooth stone, brick, glass, etc..
This would help the player get a home up really quickly since that is a bit more important in early to midgame since the player is not going to have a lot of iron lying around. For me I don't even bother using the blast furnace.
Still I like to hear what you guys think.