This has been suggested before. It won't work because you can't have more than one grass.jpg or sand.jpg, but you can bypass this by naming the textures grass00.jpg and on I believe. Still, no one has made this for a reason: limited texture count. You can only have what, eight?, ground textures per map. This really limits what kind of biomes you can make.
I've been working on a map with a pre-built medieval kingdom for a little while and it will include forests, desert, etc. so I'll probably include a blank version of the map in the file. This way you can build the empire yourself if desired.
please make it alligned with the brick grid.
You can't align terrain to the brick grid ...
would be cool but i don't know how well multiple waters or whatever would work (because you'd need a different texture for each area)
also caves aren't possible because torque terrain is ass
For multiple waters you just place multiple waterBlocks and reference individual water textures in the .mis, though it might get complicated if you didn't give names to each waterBlock.
interior caves.
Hard as hell, but it would be worth it.
Only if it's a super big cave system. To create a cave entrance and make it blend in with terrain would be pretty hard, though a bit of experimentation could pull it off.
You certainly are correct about the first part though. :D