Theo is, perhaps rightfully so, against importing what is effectively a paravirtualized Solaris kernel into the OpenBSD source code in order to run a file system.
Too sad, because the partitioning of OpenBSD is why i don't use it, with ZFS you could just do a dataset throw x^w,nosuid etc on them and give them a quota, with ffs one can bet that you run out of space (earlier or later), in one of the partitions (Workstation NOT Server).
I doubt it. Even for ports you can still symlink /usr/ports to $HOME/ports, for Scummvm with --enable-all-engines or Eduke32 (Build/GPLv2 license clash, can't be shared as a binary).