In my opinion, the worst aspect of minecraft is its terrain and how biome borders are created. It has become somewhat of an obsession for me to try to revamp the entire system, and with terrain control this has finally become possible. Basically what i'm doing is using terrain height, as opposed to the traditional system, to create biome borders. Grass biomes will work pretty much the same, but any biome which has a different top-block will be secluded by a "pseudo river". The logistics have pretty much been worked out, i'm just trying to make things as good as possible before I move on. The terrain has also seen a pretty dramatic smoothing over. My next step will be to add a few hundred more biomes all with their own custom trees, rocks, fallen trees, etc.. Deserts will be populated with more cacti formations, and rivers will include things like floating logs and rocks. Currently, the results are quite breathtaking. Well anyways i'm sure you would like to see some photos soo here.. And also, feature requests will probably be implemented so long as they lie within the realm of possibility. Cheers!
Update: The terrain generation logic is now complete
I am now into the phase of adding custom biomes, which will take some time, but a lot of it will be copy/pasting with a few edits, so mostly just tedious work..
After this is finished, I will start implementing mod support. Soo biomes o' plenty trees, patches of loamy grass, custom rock layers by biome using mod added stone... There are a lot of possibilities.
I would also like to list out a few pros/cons
Extremely smooth terrain without biome borders
A water level of 126, leaving 125 layers of stone to build within, caves are much more complex
The ability to add your own custom biomes
custom rivers with objects
some very "exotic" biomes
Grass color will have to be removed for the full effect
Some mods may not be compatible (But most are)
I can't do anything to the nether/end
If you're a fan of Minecraft's jagged terrain, then this is not for you, although you could simply edit the configs..
Update: I found a way to make this work without placing rivers in between biomes, and I also perfected my "smooth mountain" design.
Update: I applied the mountain border logic to deserts, and added a "scattering" of grass and sand to make the transition even better
Update: (I'll rewrite this post eventually lol), anyways, the 5th photo is most representative of what this mod will be in the end.