I started last year. To be honest? All the side content I haven't done yet, finally getting lucky on a house, my FC, glam, leveling all jobs to 100 etc. I don't know what I will do when I'm done with all of that, it scares me tbh.
This is what I think is a big problem for FFXIV. It's amazing for new players, you literally have stuff to do for hundreds and hundreds of hours. But it must SUCK for veterans that have been playing for years. Especially the long gaps without new content. WoW does nowadays a way better job with that.