Being the genius he is, Steve single-handedly (as far as I know) put together a great modeling program that is still in its infancy stages. There is still a long way to go, but I am confident that it will become great program.
Now, these ideas may not be necessary to the program, but it could still prove useful in many situation.
1. Interface customization. It is an unnecessary thing, but I would enjoy being able to completely revamp the interface. Customizable Icons, Color Schemes, Menu Placements, etc. (Also a revamp on the icon coloring for some very aesthetic icons).
2. Anim8or+Terranim8or. Pretty self explanatory, just everything in terranim8or put into anim8or. It would solve many errors in Terranim8or, along with improving anim8or itself.
3. UV mapping. Of course, you could always dump it into UV mapper and do it from there, but it has complications in and of itself. It would also make anim8or a little more of an all-in-one program.
4. Some mesh editing brushes, after trying out a little bit of Z-brush, I noticed the sheer genius in its making. Anim8or could benefit my so much more with this. Of course, it could not just be a replica of it, but it could have completely different tools. This would go well with (idea #2) when forming valleys, caves, etc.
5. A larger filetype support. I have to admit, Steve did a much better job than Autodesk with exporters. It would also be great if he included a vast number of different filetypes. Things like .nif, .raw, .cad.
6. I guess I could have included this in number five, but along with .nif (Gamebryo Files) niftools would also be beneficial in the next full release. This would only be useful to a very small minority and is probably not worth the overall effort, but it would still be cool.
7. Ability to merge a plug-in into the anim8or source code. It would save the trouble of that debug output, and it would save some desktop space (If that is your directory).
8. Free form select. Most other 3d programs have a freeform select, I suppose anim8or needs one too.
9. A few more primitives. Things like tube, plane, and stairs. Scripts can add these, so with #7 this idea is useless.
10. A cloth mesh, particle effect, and a liquid. Another feature in other programs that would be cool in anim8or.
Lastly, allow snap to angle to work with scale faces, rotate faces (a must), and many other features it previously would not work on.
Feel free to critique my ideas, along with post your own.