Looking at Nextcloud releases, it seems that they do a major release once a
year.
It should be possible to catch up with the upstream even if there is a
single update per Fedora release.
Update to Nextcloud 11 in Fedora 27, 12 in current Fedora 28 and then in
Fedora 29 cath up with upstream.
Admittedly that will be a lot of work, but it keeps instances upgradeable.