How hardcoded is this mechanic? Is it possible to have feats that apply effects if an Attack of Opportunity lands?
Thinking along the lines of things like the Sentinel feat where if you land an attack of opportunity on someone it will reduce their movement speed for one round.
I know there are other feats that are triggered and checked against AoO like mobility & opportunist, it would be neat if something like Sentinel could be possible, even if it's never implemented, and I perfectly understand if it's impossible to do.