@posila: For me as a graphics programmer, your post was very interesting. So far, I always implemented sprites in the Geometry Shader. But after your investigation, I think, I'll try out the method with a fixed index buffer and the sprite transformation in the vertex shader the next time I need it. ...

I prefer Proposal 4.
The simplicity of sharing both the action bar and the blueprints in one UI unit between games is just genius.

Very impressive!