Yeah, this sounds quite cool
Heres some thoughts on your ideas:
1. I can see an effective way to do this, convex mesh generation is actually not that hard to do, you could set up bones so that they have skin radius and falloff options to define how fat the body is around the bone, and how that fatness interpolates to the next bone. You can make these adjustable with a gui (much the same way as spore). This part of character generation is not too much hard work. Theres no real need to use primitives, as ogre provides plenty of mesh generation features which can be easily used (see the bezier patch demo).
2. Textures - werkkzeug3 texture edition http://www.theprodukkt.com/
is great, but requires a license to use the procedural rendering dll. There is also mapzone 2.5 http://www.allegorithmic.com
, again I think this requires a license to use the texture system in a project (however both of these allow you to use the bitmap output for free).
3. I kind of disagree here, a procedural modelling system should work in a parametric fashion eg: you never actually move or create a polygon manually, but rather you set parameters and run them through an algorithm which creates the result. If the algorithm is good enough, then it should be possible to create any type of model. Again, see werkkzeug1 for an example of a simple procedural modelling method. I think spore uses the basic principle of a spine to serve as a base for generating a mesh, again I think this is all done by assigning properties to bones, and letting the program create a mesh around it.
4. Well, generating a convex hull is again not too hard, a good space filling algorithm can be used to get a picture of the space a model occupies, which can then be filled with collision primitives. However, there is often no need to generate a complex collision mesh, in the arachnid walking paper I saw, they just attach collision spheres to the feet (to get a callback for foot placement), there was no other colllision used.
I really think the most challenging part of a procedural content kit is to produce an animation system. If you think of all the possible creatures that could be created, you would need a pretty clever bit of software to work out how a creature should move just from its bone structure and shape. That is certainly beyond my skillls at the moment, but there are papers floating around the web that give some useful clues.
there, thats my 2 cents