upgrade stable/12 -> stable/13 zfs + boot partition Mediasize 64K

Greetings,

I really want to jump from stable/12 to stable/13 but one thing is
causing a hesitancy.  And that is, my main raidz2 system has
a system boot zfs mirror pair that has boot partition size
(Mediasize) of 64K, and when I tried to zpool upgrade that pool a
year or 2 ago I got some scary message something like "boot
partition size is not large enough".  I asked about this on the
lists but never received an answer.  So, laziness required me
to ignore the problem and not zpool upgrade any of my 15 or so
zpools in the interim.

A few weeks ago I tried to make buildworld/installworld upgrade
12->13 but the boot failed in the mounting filesystems phase with it
couldn't find a bootable target.  So after restoring 12 I decided
to wait a bit.  In the interim I have upgraded every zpool but that
one system pool.  All the other freebsd-boot partitions have a size
of 512K.

So what is the current advice?  Is a freebsd-boot partition size
of 64K laughably obsolete, and I should get with the program and
repartition those disks, or can I march blindly into the upgrade?

I guess I just want to understand where these sizes are going in
the future.

Many thanks,
Russell