I think your proposal would be 'taking a sledgehammer to crack a nut'. How much harm do they do? In a full instance probably not very much. I've had people afk in groups I've joined and while that can be a bit irritating, it's up to the party leader to kick or tolerate it.
People who drag mobs over to kill afkers irritate me more. Some of them may be too low level to contribute or simply taking a well-deserved break. There is no way for the casual observer to differentiate between someone watching Netflix and waiting for the NM to pop and someone unavoidably afk due to life.
I'm sick of the salt in Pagos. Anemos got bad on occasion but Pagos seems so much worse. If afkers bother you, maybe make your own group and kick anyone who afks, or just chill, play the way you want to and don't worry about what other people are doing.

I'd like some changes to Pagos but spending dev time on finding ways to identify and punish people for going afk seems wasteful to me. If this was fun and engaging content the problem would not have occurred.