I had a pool, hence zpool.cache was present and the zfs filesystems get mounted as expected. ZFS works to a certain extent (zpool scrub panics straight away, but I was able to tar off to a dataset a fairly large tree (the pkgsrc tree actually). In this case I was messing with a pool on a ld0 device attached to a nvme controller under -current (VirtualBox VM).
The thing is, zfs does not seem to have volinit subcommand. It is not documented in the man page, neither shown by 'zfs help', and the pool gets mounted anyway, even if I have this line commented out.
Chavdar