You could get a quick zoom in, a dramatic slow down of the opponent doing its thing and then you could just quickly click left mouse button to confirm the reaction or the right one for a "Pass").
I am against any type of forced zoom. Was nauseating enough in Skyrim but could at least be modded out. Not sure that would be possible here if it is part of an actual mechanic. I can imagine it would get annoying for most people anyway since it would happen on every turn for every enemy until you run out of spell slots.
Niara has a good point, but I think with the clunky interface we have Zellin's idea is pretty good. Something similar could be just a Reaction button, maybe it lights up or something, but when we click on it it acts like the current spell buttons where we then have to click again on what level spell, only we would be clicking on what type of reaction instead. All reactions of all types would go here rather than on the spell bar. Personally I would prefer a popup menu, but if this was added it should be able to be toggled off for people who don't want to deal with it.
