To clarify, based on both the Rich Errors talk, and the Outference talk:
The initial prototype for rich errors will not support generic errors. However, generic errors are planned, and are part of the intended design, but they have to wait on the outference getting implemented.
Is that all correct? If so, I'm very excited because watching the Rich Errors talk, I was quite worried about the amount of limitations on them, but if those limitations are only in the initial prototype, then phew!