As I recall, it was something Positron had talked about doing in the future, and I recall him mentioning that one of the issues with making customizable animations was modifying the database to give the ability to make the power origination points different. In the OP's example of a powered-armor suit with built-in weapons, having a gun mounted on the back of the forearm, so you stuck your arm out and the gunfire visual started at the back of your hand.
Since this is a fairly serious alteration to the power and character databases on top of just the coding for the different origination points, I suspect that it's a pretty long-term future enhancement (on the basis of 'if it were easy, the original design team would already have done it, just to make the game more awesome').
I suspected it wouldn't be simple. Thanks for the education.
Would it be simple to just change out the emotes and keep the AR gfx without changing where they come from?