Had a look at Moho and it's Smart Bones today, specifically some examples for vectors where they interpolate between different states.
Obviously with bitmaps we cannot have this flexibility, but it certainly would be nice, in addiiton to being able to go to different images or attachments, but also to interpolate things like scale, rotation, transform based on the bone rotation. I guess that is what you mean!
I think its definitely an interesting way of working and something I look forward to seeing. Whether it is scale-rotate-transform interpolation, or flipping through a defined list of attachments (with the ability to order them) it would be very interesting!
Smart Controller? Don't know, but would love to hear others' thoughts.