It certainly could, but would probably best be done with additional volunteers. Perhaps you?
Duplicati is completely dependent on what volunteers can do. Recently, the focus is stability.
There’s not much point in having easy backups that don’t work reliably. Duplicati is still Beta.
This should probably not be part of the feature request (open a support ticket if desired), but
would have IQuotaEnabledBackend if SFTP could do quota. I see some signs that it can in version 6, however Duplicati uses SSH.NET which doesn’t talk about quota in source that I can find, and is also getting kind of old from a good-crypto viewpoint. Let us know if you know any good free SFTP clients.
Dupilcati Server is a thread from today talking about a more appliance-like (but still split client-server) approach, as well as the too-large-to-handle number of other possible approaches that people take…
There has been at least one attempt (I forget its name) to bundle storage software to get near that idea.
EDIT:
SFTP - check free space available has more on SFTP version dependency, workarounds, and Renci.