Sharing code across separate teams seems like separation in name only. If you can draw a line at the HTTP boundary with a back end api and a front end app, everyone should be happier. Only you know if that's vaguely feasible with your current architecture. Story acceptance on an API requires a slightly more technical PM and some education from the developers, but give you a very easily testable border and the ability to add mobile or other interfaces at a much lower cost.

Matthew