I've also been running my own federated XMPP server for a few years. To my dismay I discovered about a month ago, that a Gmail user on the "new Hangouts UI" never saw me as online. I could send them messages but they just got dumped into an "email"-looking message within Gmail, which I don't think even registered as unread. You'd have to go looking to find it at all. I think they could send me messages, but why would they if I never appear to be online? If the Gmail user reverted to the "old chat", things seemed to work as expected. They're nice enough to let you toggle between them for now, but my friend said only the new interface allows free SMSing or something.
Don't take my word too heavily, as this was just what I saw in a quick test with one Gmail account of my own. But I decided if Google is going to basically hellban me, and since almost all of my contacts are on Gmail anyway, I'd just transition to a Gmail account to talk to them. I only have one contact that's not on Gmail, and it's an acquaintance I'll probably not talk to again. Maybe I'll keep the server running just for decentralized geek-cred. At least Google is nice enough to let me use a desktop client, for now.
I also noticed Google doesn't seem to support encryption on federated chats. I guess the proper solution is something like OTR anyway, but that was disappointing to see.