Extend https://wiki.gnome.org/Sysadmin/NextCloud to mention also calendar and addressbook shares using Evolution, as part of the desktop integration. In particular setting up a collection account in Evolution.
Mention on the same wiki page what needs to be done for better integration with Gnome, in order to motivate people working on these features, providing (the installed) NextCloud supports the protocols:
-- Nautilus: For setting the shares implement a WebDAV ACL editor
-- Evolution: add ability to discover the home sets of other users (for calendars and addressbooks)
I personally use a (Web,Cal,Card)DAV server, that in not NextCloud. For an organisation to use open protocolls/standards, it is essential to have software, that speaks the protocols and that the software has also the notion of “other users”, who share data. Users shall be able do accomplish everything without having to visit some webpage. I think the two features above are the most urgent ones.
Once Gnome developers start using these features facilitating the collaboration, they will add more.