probably not

I can’t even think of a feature (other than compression/encryption but there are better ways) that a watch would use from zfs.

I imagine the main reason to use it would be that you have ONE filesystem that runs everything, everywhere. Though come to think of it, I feel like snapshots and relative ease of creating new filesystems in the pool could be handy for upgrades.

Zfs still has a huge overhead. It needs more ram than a watch or even phone is going to have - until they start packing enough that losing 4gigs of ram to overhead is fine.

the author of it here, hi ;-)

Yes, ZFS on Boot is right now more like a technology preview. Fonts break badly, so ZFS boot is not advisable (and also doesn't give you that much benefit really).

I want my data to be guaranteed to have integrity and really enjoy snapshots (I've been bitten by Final Cut Pro X data deletion errors etc and rolling back a snapshot is a bliss).