This'll probably take some doing but like.... does anyone even USE skype anymore? And google+ is totally dead. Might make sense to put fields for Twitch, Discord, and I realize i'm probably in the minority on this but mastodon as well would be cool.
A pronoun field somewhere might be also helpful for people. There are probably scripts for freeform textboxes that let you type whatever? There used to be for vBulletin at least.
Custom user fields should be easy to do, from what I remember of running another phpBB board over a decade ago. I'll try to have it in before the rsync tomorrow.