Just for the sake of experimentation, I’m curious to see if it’s possible to do my 2-D Nape platformer using Away3D instead of Starling for graphics (all non-graphic-related things being the same).

A couple of questions:

How can I access Nape’s ShapeDebug from an extension of Away3DState? I thought accessing it through StarlingState was complicated enough. 

How can I continue to use Flash as a level editor via an ObjectMaker? Can I continue to use ObjectMaker2D in a way that Away3D will accept, or is it even possible?

The Away3D website claims that Away3D can integrate with Starling. Could I put 2D sprites in a 3D world, Paper Mario-style, or is it more for overlay/HUD-type usage? Would Citrus need a new engine that includes both Away3D and Starling at the same time for that to happen?
klingelton mp3: https://klingeltonemp3.info/

If you use any as3 api that renders using stage3D, you can combine them.
The only thing required is to ensure that none of the api clears the current rendering after its done.

using away3D you can simply set view.shareContext to true
and “manually” define the rendering passes and order from your views/apis

here for instance, an example where you render 3D objects, clear the buffer so the next 2d “layer” is rendered on top.

stage3DProxy.clear();
view.render();
stage3DProxy.clearDepthBuffer();
   
otherviewOrExternalAPI.render();
stage3DProxy.present();

so the only work if you use away3d for the rendering, is to know how to call render in your api and prevent it is clearing.
Away3d also has sprites if you need 2d sorted into 3D.