There is no way they're going to add in a reaction system that slows down the combat. It's clear from this patch that they're trying to speed up the combat as much as feasible. Hell, the animations are almost too fast in my opinion, but i'll take it if it means I'm not just sitting around watching 10 different ai take their turn for 70% of the combat. I say build it in to the mechanics and have it be automated/simplified.
Doesn't seem like Larian is going all out on speeding up combat to me, nor do I necessarily agree on the animations being too fast.
The Warlock Hex spell is a glaringly obvious missed opportunity for streamlining for instance. Changing the spell to automatically curse all abilities (either full disadvantage or a smaller flat penalty) would shave seconds and annoyance off of almost every round playing with one or two Warlocks. Currently this gets old really fast given Hex is likely the by far most cast spell in the game alongside Hunter's Mark and given the ability curse is a useless time-waster in 99% of gameplay. This is an example of appropriate homebrew (cRPG adaptation), but Larian isn't having it for some reason, 5 patches in and all suggestions have thus far been ignored.
The Dash animation is another even more obvious example; making Dash a magical caster animation is a needless waste of time besides being unimmersive and counter-intuitive. If you sprint, you don't waste seconds summoning shining inner strength - you simply get on with it. In general, non-magical animations should be shortened and made to look more natural.
Counterspell, even attack of opportunity, could like others have mentioned, be made into a zoomed-in slow-mo interrupt mechanic similar to Mass Effect's paragon/renegade interrupt system. Obtrusive and unimmersive reaction mechanics definitely aren't a necessity.
