In the good old days of ICQ and Jabber you could install a client that would integrate several protocols into a single lightweight UI (e.g. Miranda IM). Unfortunately the new wave of messengers is much more successful at guarding their protocols against such integrations.

That said, I wonder what's Discord's official stance on such things. Their bread and butter is voice chat, and they seem to be fairly open minded. Maybe they will eventually provide a public API for basic text messages.