Earlier quoted context omitted.
> XMPP is the pinnacle of chat that just works. Except no. You can't even have a conversation between Conversations and Fluux because OMEMO is enabled by default in Conversations and there is just no OMEMO support in Fluux - despite it being actually modern one. Gajim works but Pidgin doesn't even show "I sent you an OMEMO encrypted message but your client doesn’t seem to support that". Just like images, which is a f…
And of course most XMPP clients which support OMEMO only support an old version of it, which is incompatible with the new OMEMO version, currently only supported by KDE’s own client—Kaidan. That also happens to be the only desktop client I feel like I’d actually enjoy using (if only I could use it to talk with people not using Kaidan).
Anyway, there is a discovery mechanism, and clients do adapt the version used by peers, so there is no incompatibility. Kaidan choose for a while to have only OMEMO:2, because resources are limited and they were going for the latest version first, but resource are limited for everybody, and it took times for others to implement OMEMO:2 too.
NLnet/NGI did (and still does) gave financial support on several XMPP projects (including mine, huge thanks to them), and, curiously, when there is money to help, implementations happen. That's problem nb 1 with XMPP: lack of financial resource.
() GUI (notably web UI) is being reworked, not stable yet, but the CLI is pretty solid.