I've been thinking about this stuff for a while, the fact that Larian doesn't want interruptions/pop-ups because they consider it "disruptive to the continuity of the action" or something (which is a bit bizarre in a turn based game where the alternative at interjecting the combat with your actions is... To watch NPCs move on their own, if you ask me).
I've came to the conclusion that this is probably a matter of presentation more than mechanics for Larian.
To be more explicit, I think that what they think is more or less: if we are going to implement reactions, they need to look "sleek and cinematic" in line with the rest of the game rather than just being a crude and unappealing "YES OR NO" pop-up over-impressed on the screen on a regular basis.
I'm honestly not sure how I'd solve this. I've been trying to imagine ways they can do this and "make it look good for the casual player", so to speak.
A very quick camera close-up and slow down before prompting you for confirmation?
Offering a short time window like a QTE rather than literally pausing the game?
I'm not really sure what could work without being an even worse problem than the half-baked automated reactions we have now.
I've been mostly thinking about how XCOM 2, which is probably the current pinnacle of production value when it comes to a turn-based tactical, would manage this.
That game has ONE type of reaction that is not automated, and it's a skirmisher skill that simply gives you a "micro-turn inside the enemy turn" instead of an ordinary automated overwatch. But even that is not an exact match, because that's about doing whatever you want with that action, while reactions in D&D are about confirming a specific type of attack on a predefined target.
