LXC/Incus is not a moonshot. It’s perfectly usable solution. If you want to see benefits, you can read them here: LXC/Incus support in TrueNAS Scale
Also you misunderstood what “not on roadmap” means. It just means it’s not currently planned because focus is elsewhere. It doesnt mean that it will not be ever included if there is demand. That’s why it is in feature requests, to request putting it in roadmap.
Systemd-nspawn is pretty low-level, without many features and you also have to maintain wrapper so it’s actually user friendly.
With Incus you can depend on already user-friendly solution with big user base and active development.
Incus would offer more features and would be easier for iX dev team.