I'm with Jeff on this one; the capability is well within the ability of the current Di2, and there is a demand (as long as you call it a 'training aid') I'm sure this will happen eventually. It would be integrated with a power meter of some kind, and the sophisticated on-board computer will make all sorts of choices for you to optimize your performance.

I'm not saying that it's going to be wide spread, but since it seems to be only a trivial software problem away, I can't imagine something won't emerge.