I remember playing Icewind Dale 2 and more recently Pillars of Eternity and setting the Pause setting to trigger on pretty much every instance. So that it played sort of like a Turn Based game, but that I did not have to control or micromanage EVERY single party member's actions EVERY single round. This was due to the fact that these games had decent AI settings that meant that they already had default actions every round based upon their own positioning, other party member positioning, their own own health, other party member health, and the enemy's health.
So Blindhamster, you asked how would RTWP work with Reaction abilities? In my mind, its simple. Give each individual character a single reaction each round (per the rules). Then include settings that pause the game for the most common triggers of reactions, namely those listed above. Its not that complicated, although in my opinion RTWP is only really worth it if you include decent AI settings for each class that automatically know when to use their reactions (spellcasters using counterspell or shield, rogues using sneak attack, etc).
That's true. A RTwP implementation could totally have an auto-pause on Reaction Opportunity.