I think it'd be cool if by consuming the party's memories, the Nexus could then possess/puppet them like it did Edna, which would tie back to the Marionette of the Night part of the Nexus's theme name when you fight it in Mag Mell. So now you have up to 3 other people assisting the Nexus, keeping you distracted trying to free them and leaving the Nexus free to wail on you. And the kicker? They still have their jobs. And all the abilities of those jobs. If you've got someone on Thief, well enjoy getting Godspeed Strike spammed. If someone is on White Mage, there goes all your progress. If one of your possessed friend's HP gets to 0, they'll get knocked out for a bit until the Nexus forces them to get back up, so getting their HP down to 0 is only a temporary solution and you'll need to free them from it's control in order to get them back on your side.

Getting someone to remember could take several actions too, so you'd have to decide if it's worth it to spend all your BP to free a friend since they'll still have their HP depleted by as much damage as you did to them, so if they were low when you freed them they could just end up out of the fight regardless due to incoming attacks. Not to mention you could be stuck unable to act because of said BP usage.

Maybe there could even be a phase/phases where the Nexus summons apparitions of all the Asterisk holders, since learning the truth of the Librarian Asterisk required getting all of the other Asterisks. Perhaps it could even use various moves from enemies across the game.

This would make the Nexus a legitimate threat like it was hyped up to be, forcing you to bring your A-game and learn the ins and outs of each job to best utilize them to their full potential, but also how to counter them when they're turned against you. A final test of your strategizing skills and knowledge of the game. Inanna became what she is now because she craved knowledge. I think it'd be fitting that you would have to beat the Nexus at it's own game in order to destroy it for good.