I have a simple mod for 1.12.2 which replicates vanilla 1.6.4 cave generation, including mineshafts (optional); together with a dungeon count of 16 you can pretty closely replicate 1.6.4 seeds in 1.12.2 (dungeons will not be the same since in 1.7 they doubled their range from 128 to 256, which is why I recommend using Customized to double the count to 16. Ravines are also different but in the same general locations and with the same frequency, which was unchanged):
Of course, if you are looking for a Forge mod then that is an issue since I just edited the bytecode (it may still be possible to use it with Forge since all I changed was some hard-coded numbers, not the code itself. It is even possible to edit it yourself to customize caves to your liking; I changed the numbers on lines 7 and 18 from 15 and 7 to 40 and 15 respectively; the first number controls the size of cave systems while the second controls their frequency, with the average density being (size - 1) / 8 / frequency, or 0.25 and 0.325 respectively. The larger both values are the more cave density varies. I recommend using Unmined to easily see the effects of changes).
Note that this only works for 1.12.2 although it would only take me a few minutes to make a version for 1.12 (mostly finding the right class).
title says all, Any mods out for 1.12 that makes caves bigger and better again?
Bump
I have a simple mod for 1.12.2 which replicates vanilla 1.6.4 cave generation, including mineshafts (optional); together with a dungeon count of 16 you can pretty closely replicate 1.6.4 seeds in 1.12.2 (dungeons will not be the same since in 1.7 they doubled their range from 128 to 256, which is why I recommend using Customized to double the count to 16. Ravines are also different but in the same general locations and with the same frequency, which was unchanged):
http://www.minecraftforum.net/forums/mapping-and-modding-java-edition/minecraft-mods/1292668-1-7-1-9-themastercavers-mods-and-tweaks
Of course, if you are looking for a Forge mod then that is an issue since I just edited the bytecode (it may still be possible to use it with Forge since all I changed was some hard-coded numbers, not the code itself. It is even possible to edit it yourself to customize caves to your liking; I changed the numbers on lines 7 and 18 from 15 and 7 to 40 and 15 respectively; the first number controls the size of cave systems while the second controls their frequency, with the average density being (size - 1) / 8 / frequency, or 0.25 and 0.325 respectively. The larger both values are the more cave density varies. I recommend using Unmined to easily see the effects of changes).
Note that this only works for 1.12.2 although it would only take me a few minutes to make a version for 1.12 (mostly finding the right class).
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?