I consider XMPP/Jabber integration in SFOS a real plus and a great way to avoid being sucked into WhatsApp. However, there are 3 features that should be supported OOTB to make XMPP/Jabber a real alternative:
end-to-end encryption (OMEMO if possible)
sharing of media files
and
group support.
I know, some of those features can be ‘retrofitted’ by installing corresponding packages like telepathy-gabble-plus, but let’s be honest: that’s not an alternative for “non-nerd users” . And: I don’t like the idea of uninstalling and re-installing packages with every OS update too much.
Adding XMPP users from SailfishOS’ own GUI should be part of this (see comments at bug report XMPP no longer works), because that’s a really basic feature, that’s definitely missing!
I find XMPP the most reliable federated instant messenger on mobile especially in 1:1 chats and I think the messages app is starting to be the last XMPP clients without support for OMEMO. I would also like to add links to the specifications.