Fluxer, while promising, is currently too buggy for people to switch to, and still has an unproven back-end that needs to show it can scale up. I am hopeful for it though, as it uses GPL, and the dev plans to implement federation and encryption at some point.
XMPP is rapidly gaining Discord-like features thanks to the Movim client, but it too is not yet a 1:1 replacement. It is however pretty stable, and could be used while users wait for those additional features.