sysexts are indeed a very interesting feature, though it really only complements some other whole-system solution since it can only affect files under a non-root folder location.

I'm struggling to see how sysupdate is really equivalent to bootc or ostree though. Sysupdate is just the sw-update tool from Yocto that's been around for 10+ years with a little more syntax sugar, which itself was just a common shared implementation of what all embedded systems had been rolling-thier-own of for almost 20 years before that. It says it requires an A/B/.../N partitioning scheme, which is exactly what bootc/ostree/etc is designing to avoid.

If you don't use the whole disks update thing from sysupdate, then instead you're just talking about a transactional package manager that is still in its infancy and hasn't addressed the many gotcha and corner cases that the dozens of more mature package managers have. It's not actually "transactional" in the sense of undo for example, it's "transactional" only in that you won't get partial install, which hasn't been a problem with any existing package managers for almost 40 years. All thier listed things you can list together for a "transaction" association are either things that are already linked via existing package maager packages, or are only useful for embedded systems.

I'm not saying sysupdate isn't useful, upper end of embedded design is pushing into the space where systemd is standard now so it could be useful for those devices, but it's not really equivalent at all to bootc/ostree, and doesn't really have amt applicability outside initial system imaging from a live disk, or embedded devices.