In the end it is mostly a matter of time (and head-aches) for Larian to develop this. Imo it would make sense for them to do it if it is usable for the wider audience. As such starting with an on / off overwatch concept to slowly implement an on/ off / targetted depending on the spell would be a big win for everyone.
Yes, a matter of time (and headaches), but based on the overwhelming number of Reactions posts, it is VITAL to the overall game that they get this right. So yes, it's a headache, but if they screw this up, they will literally ruin the game for a lot of people.
Too many popups/prompts will drive people who hate them away from the game.
Too few popups/prompts will drive people who want them away from the game.
There must be balance between the two. It may be a headache to develop this, but it will be 100% worth it in the end. The more intelligent they make it, the better the end result will be. Slap a bandaid on it, and people are going to throw in the towel and blow fuses.
I'm telling you, if I don't have a decent working Counterspell in this game, the first time an enemy successfully blows up my party with a bottle of grease and a Fireball, I'm going to blow a fuse if it's because the game had me cast Counterspell on something stupid like Beacon of Hope OR I'm not able to cast Counterspell because my mage used Shield against an enemy who only deals 5 damage on average. I'd MUCH more prefer an absolute prompt system like Solasta than have any of those scenarios occur because of some poorly executed presets/automation.