Eh I'm not a fan of slowing things down for reactions. The game is turn based, so it should stick with turn based and not add psuedo Quick Time Events. In a turn-based system, I expect to be able to leave my computer at any point, and come back not having missed any opportunities.
I'd prefer that time froze and a pop-up window appeared asking "do you wish to use [reaction]?"
I guess if they can slow down and add a timed popup... They can easily pause this moment and freeze the game until you click that popup.
My fear with a pause is that it would be like... In Solasta. I love this game but those pause appear more than once on every turns. I can deal with it but I don't think lots of players would like this.
I hear you, and that's why it should be an option like others have said. You can choose either toggle reactions or pop-up reactions. I suppose Larian could also add a third QTE option, but if I had to choose between pop-up or QTE I definitely choose pop-up. I like the pop ups in Solasta. They only get to be slightly too much when you have a Paladin plus characters with the Protection fighting style.
Even then I think it's fine, I love the options. I truly hope they implement OPTIONS for it! =)