Unless this slow-mo effect continually slows down until time stops completely, this method would require a time limit for making any reaction decision. In which case I strongly disagree. This is a turn-based game; absolutely nothing in combat should proceed without player input. The fact that the game doesn't automatically enter turn-based mode when a trap activates or that it leaves turn-based while characters are still making death saving throws are already bad enough.
Swapping to give you control of said character would be helpful in cases where you can choose between multiple reactions (instead of multiple sequential pop-up windows), but it's worse for situations where you only have 1 option. For these cases, the game should simply give you a pop-up instead of forcing you to search through your hotbar for the only available reaction.
No time limits, after slowing down it eventually stops, requiring an input from the player. But the problem is how to inform a player what kind of input is required. Small pop up near the reaction section maybe with allowed reactions being highlighted. Idea is that the player will eventually get used to this and will react fast enough for picture not freezing completely. I personally don’t like this freeze moment, it gives me a feeling of accidentally pressed ESC during an intense action.
