There seems to be this assumption that in combat, reactions are going to be popping up all the time. Is there anything to suggest that this is the case? Most of the fights that I've been in, I don't use any reactions at all. There just aren't that many opportunity attacks getting triggered. And if you do use your reaction, it shouldn't ask you anything else until your turn comes around again (for each character you control).

I'm just not convinced that having it ask you whether you want to use a reaction is actually that cumbersome. And for those who think that it makes combat longer, I would argue that being able to use your reactions effectively might actually shorten combat by making you more efficient. Again, something I don't think we can really know until we try it.