Libervia (on which I'm working) does support OMEMO:2 (it was actually the first client to implement it) + legacy one + OX (OpenPGP) + OX for Pubsub (so you can encrypt everything pubsub related: blog, forums, tickets, etc). ()
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.
XMPP council (disclaimer: I'm a council member for the current term) asked me to some modifications and to re-propose, which I'm about to do. I couldn't find the time so far (cause I'm working on ton on stuffs), but will go back to it very soon.
And Libervia (disclaimer: I'm the lead dev). It also implements SFU including components (based on Galène), but I'm reworking design on this part.
Also note that Libervia is using a backend/frontends architecture with a D-Bus API, you can use it to make your own frontend with any language you like.
Yes, I'm having a DDoS attack these days, no idea why somebody would do that to my small server. I've deployed counter measures so the site is more or less usable, but the attack is still going on.
And the team is nice (I've met some of them at PyCon or FOSDEM).
The framework is pleasant to use, and there is a descriptive language, kv, which is really great.
Cross compiling may be painful though (I did it for Android) and the app loading time is a bit long, but it's working.
Some things may be missing in comparison to big frameworks such as Qt, there is no WebView for instance, and accessibility is unfortunately not as good.
It's overall a very good project and it's a pity that it's not more known and used.
I used Kivy once a few years ago for a device that had strict constraints on what it could run with the requirement to run the same code on desktop too (to display the same data). It worked very well for that.
It was not an elaborate app, so I cannot comment on how well it might work with something bigger, but it worked very well for what I needed.
It's pretty new though, and it's a bit rough around the edges still. The other issue is that almost every single package/library for pyside6 only supports QtWidgets, not QML. Meaning you wouldn't be able to use tons of libraries that make up the python qt ecosystem (for example, pyqtwidgets or vispy). Not a huge dealbreaker but it's something to keep in mind.
Yep I don't think there's a practical way to use qtwidgets on mobile, so it's not like Qt is treating pyside differently. It's just that the ecosystem doesn't really follow. I wonder if that's different on the c++ side. Is QML more prevalent in the c++ qt ecosystem?
Thanks for sharing your experience and links! Based on plyer's GH, it looks like you could use it to develop an iOS and Android app. If it supported more APIs (like Health Kit, accessibility), I would try it in a heartbeat.
I'm using XMPP for chatting of course, but also for blogging (my blog is XMPP based), A/V calls, events organization, file sharing, photo albums sharing, as a remote (with ad-hoc command, I've even built an specific UI to control MPRIS supporting player). I'm building an agenda, a forum, a generic list tool (TODO, shopping list), and other stuff.
I'm using Snikket to host a small server for family and friends, with accompanying mobile clients.
I've also built an XMPP <=> ActivityPub gateway (soon to be released, but dev version is already available), so my blog is accessible from any AP supporting client, and I can access the AP ecosystem (including events as seen in Mobilizon).
There is Slidge IM if you wanna talk to legacy network such as Signal, Whatsapp, Telegram, Discord, Mattermost, Steam, Skype, Facebook Messenger, Matrix, VoIP.ms.
There is Biboumi if you wanna talk to IRC.
There are old and new email gateways on the work (I'll be working on one myself).
XMPP is used in many fields (from healthcare to games), you can have an idea at https://xmpp.org/uses/instant-messaging/ but I have the feeling that this list is not up-to-date and is incomplete. I think that it's used in Fornite for instance.
So yeah, we may not be the best for marketing, and we not have as much resources as we should, but XMPP is still well alive and kicking!
XMPP does use Atom as its (micro)blogging format (XEP-0277), and making followers/following lists (subscribers/subscribed in XMPP terms) public is opt-in with XEP-0465.
Note: I'm very involved in XMPP, and the author of the latter XEP.
Edit: forgot to mention that it's also available to ActivityPub thanks to the XMPP <=> AP gateway (that I've authored too)