Well, i really do like tactics trainer and i think an opening trainer one that would have you make a move in the opening and tell you better moves... eh just a thought

nice but ideas and theory in opening are always changing and largely opinionated most of the time so just like opening books it wont be of most help.

Yeah, but we can surely agree which ones are just positionally better... or when your making an obviosoly bad mistake... i admit it would really be mostly for new players though

They have something like this already for several openings, as individual courses in Chess Mentor.

We have "plans" (very loose) for a "repertoire manager," which is in the same general area as the OP's suggestion. I'm not sure when we'll get to it, but it will be a cool addition.