Marrying npcs.

[Cherub]

Or they could bring back the Path Companion concept that 1.0 had. Before that though, FFXI had something similar, called an Adventuring Fellow. Aside from being able to fight with you out in the field, you could bond with them and change their outfits depending on said bond. They each had separate personalities, much like when you choose a retainer in XIV. I would like to see something like this return, instead of just having a battle bird.

If the companion concept woule have a relationship system, I'd probably spend more time in XIV to max out the relationship than I ever have before for any other grind.