Congrats to the team! Long time irssi user here, I've tried to move to several other clients over the years (for change's sake rather than any real reason), but nothing ever "stuck" with me.
irssi-relay allows you to connect weechat's relay clients to an irssi instance. I don't think it's gotten much use outside the few of us that work on it, more eyes are of course welcome.
Please file an issue if you don't mind (and if you can dig in and try to find the problem or even fix it, so much the better!)