Why wouldn't it happen? I would be fine with a QTE, like a skill button to toggle anytime during the enemy turn to react. I don't really like the turn based argument since the fluidity it would offer is barely a compromise to me.
But QTE doesn't solve a thing! If anything it would slow combat further over a popup as you would need to wait for the QTE to finish rather then dismissing it as soon as it appears. Make dismissal of reactions easy - space, RMB, O on the pad. Anything easy to press. You know you don't want to use reaction, it will be an instinct, popup will be gone within a second.
Fluidity is a matter of presentation, not artificial time limit - reactions won't become any more fluid because you need to wait couple seconds for them to expire. You can make choosing things from
a menu "fluid" if you present it right.
Whatever the solution will Larian come up with, they need to give players a control over the reaction - when on on whom it triggers - and make their impact on combat clear. That is especially important for defensive skills, which IMO are greatly underappreciated in BG3.
