I have a few ideas for blender 2.5. yeah I like to think ahead.
Anyway I divided it into 3 areas which I think could use improvement.
Vertex Painting could use a rehaul, its a little slow and the colors you paint with don’t always show up the actual color they appear as when they render. Also more display modes for vertex painting (a shaded view would be nice) and an alt color selection so you can use two colors at a time.
A way to paint directly unto the models surface, including procedural textures, specularity, and transparencies. Modo 201 will be able to do this and its a very attractive feature imo. It would be great for cartoon style animations where your not going for photorealism. Also a way to output the textures as a uv map. Although if a blending option and layering was possible, realistic texture could possibly be achieved.
Wacom tablet support for texture painting
Camera filters, and control over Depth of Field like Yavray for blender render
Multiple passes (I think this is being considered?)
Hard body Dynamics
Eisner Splines (Great for Squash and Stretch)
I have a few lighting ideas too, but I need to get back to school to use maya again. It had some great lighting features.