Hi Peter, Pierre-Luc,
thanks for sharing your suggestions! I am planning to submit a proposal for the 3D tool, and a bunch of ideas similar to yours crossed my mind, too. I think first of all we need a decent implementation of the fundamental aspects of the tool (as described on the webpage I prepared for my proposal; see my recent post).
But as soon as this works, I believe it would not be too hard to add features like extruding 2D objects (arbitrary paths, possibly) in the direction of VPs, using the pen tool to draw on inclined planes (these could be defined as the faces of some 3D box), and similar things. Depending on the timeline this probably won't be part of the SoC project itself, but it would be great to work on it afterwards.
I am going to include some ideas in my proposal (should hopefully be finished by tomorrow night; German local time, that is ;)). Any further suggestions are very much appreciated.
Cheers, Max