First of all there is some kind of reaction rework incoming so hopefully we will be seeing it soon.
What you describe is a surprisingly common suggestion. I don't like the idea - mixing turn-based and dexterity based gameplay always feels unpleasant to me, and I think people underestimate how much it would slow the game down to give players a window of opportunity to manually trigger reactions. It would need to be made clear that players HAVE an opportunity to trigger reaction, so the combat would need to be slowed down anyway to give player windows of opportunity to react. I am also of belief that popups wouldn't slow down things much as long as they are easy to dismiss (like just pressing O button on gamepad, or RMB). Making the whole suggestion potentially very costly to implement and troublesome with no clear benefit that I can see.
Good compromise for Larian?
Personally, I think the current implementation sucks for reactions and reactions alone - by that I mean actions that player can take in response to what enemy does. I can't imagine those working well, without a popup system. Stuff that is initiated by the player, so - so stuff like sneak attack, smite etc. - is to me acceptable with some streamlining. Player decides when and on whom to use it already, so while some depth is lost, and that is a shame, but it is in player's control.
