If you won't drop the other networks there's no need for them to join your server, your still on the networks they're already using. Only you can change that.
I'm currently relying on the Signal rework of TextSecure to get most of us off of Hangouts: the big barrier to adoption has been easy-to-configure clients that work on Android, iOS, and desktop and sync message history amongst clients.
The craziest thing I get asked is "Do you have WhatsApp? I can send you pictures, and it's FREE!". Oddly the thought of sending an email with a picture attached (how easy is it on a phone these days??) doesn't pop into their mind as being "free" either!!! Insane! Email is far superior, as I can archive it unlike IM history.
nod nod
I mention in another thread that if Signal (nee TextSecure) doesn't take off, perhaps what we need is a super-sexy frontend on top of SMTP and IMAP.
> ...Do you have WhatsApp?...
The thing that really gets me going is the folks who will only send pictures with MMS.
But there are still open issues. One big one, compared to all the FB/Google/etc. offerings is the ability to have a usable chat log. Current xmpp implementations/standards are more or less useless if you happen to use more than one device and want to look something up/want to see what you wrote to your brother yesterday, on your desktop, while looking at your phone.
Mandatory extensions in my world: - Stream Management (easy) - Carbon Copies (easy) - MAM/Message Archive (described above, hard, haven't found a way yet)
It should be in prosody 0.10 [1] (not stable yet) but I did not yet have a change to test it.
(And XEP-0313 is still quite new and experimental)