Is that a desirable outcome? The point of the 3 action economy is to provide options and encourage movement and other non-attack actions (hence the -10 penalty for that 3rd attack). By forcing people to hold on to an action for that reaction, you slow down combat and make it less dynamic and interesting. or, at least, that seems like it would be the outcome. I have not played PF2E yet, but the one things that gets almost universal praise is the 3 action economy and so I am inclined to think messing with it can't be better than they way it is.Maybe, I don't know why it would be any more chaotic than the current system. This is not my ideal, but lets just say we keep the 3-action system and we only change reactions. So now, a reaction cost 1 action. If you use all 3 actions on your turn, you can use a reaction to make the OA or cast counterspell (I assume it is a reaction in PF2e). Now there is a solid reason to hold onto an action.