Backup a certain Snapshot of an Instance

I saw there are some discussions about lxc export vs. lxc publish container.
lxc export [<remote>:]<instance> [target] [--instance-only] [--optimized-storage] [flags]
lxc publish [<remote>:]<instance>[/<snapshot>] [<remote>:] [flags] [key=value...]

One feature missing in export, is the ability of aiming a specific container/snapshot as source.
lxc backup takes either container as source or container include all of its snapshots.
Is there a way to create a backup from a container/snapshot?
This would produce a downloadable backup tarball from a container/snapshot in one step!
The lxc publish way would be to create an image first, than publish that image.

It’s not very practical to implement because backups are tied to instances and so can’t easily be tied to just an instance snapshot. All the export logic also works with a full volume (and possibly its snasphots), doing this with a snapshot alone wouldn’t be trivial.

On the upside, there is an easy workaround you can use, copy the snapshot you want into a new instance, then export that. If you’re using a storage backend that supports copy on write (basically anything but dir), this is pretty much free and very fast.