Although I've got pleanty of my own code I need to be working on, I could probably help with the archetecture. By naming those interface classes it looks like you're planning on using some kind of COM archetecture. In the games that I've worked on, we've always just used a well structured object hierarchy, so I might need to read up a bit on COM, or see how you're coding things together.

I don't suppose you have any more detail documents than what you have posted here. I can imagine how things could work starting from how JJ2 works, but I'd rather not assume anything. You really need to specify where exactly the 3D functionality will be used. Just putting a bunch images on quads and using them like sprites isn't necessarily the best way to use the system. Also, be aware if you want to start animating these sprites using the traditional multiple images as frames, that can take up a lot of memory. You don't want to be half way into the project and realize that all your animations take up over a gig of video memory. (This actually happened in one of our projects. Thankfully it was already in 2D.)

So if you could fill me in on details and ask what you want from me, I'll be glad to help whenever I have the time.