>If someone gave them a filesystem with the right license, ideas from 20+ years ago and a promise to maintain it on OpenBSD forever, I'm sure they'd take it.

They have the right to take NetBSD's UFS (with WAPBL), FreeBSD's (UFS with softupdate) or DragonFly's Hammer2.

Or give users the freedom to use ZFS (optionally) like NetBSD.