I agree that sneak attack needs to be improved, and with the new reaction system implemented with patch 9 it feels as though we now have the core elements of a mechanic that could be used to achieve this.

This has been discussed on this forum before, most recently, I think, in this thread.

"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"