So there is precedent for this, but we live in very different times now.
That's a wonderful idea. In fact, we've had such a standard since 1999 (protocol codified in 2004[0])
It's called XMPP[1]
In fact Google Talk, Facebook Messenger and Skype were all either based upon, or supported XMPP...and now don't. Slack used to support IRC and not doesn't. There's a term often credited to Microsoft that also applies here: embrace, extend, extinguish.
You're completely right that messaging clients is regional, but it's even more regional than just "Europe". I'm always confused when people claim that WhatsApp is huge in Europe, because I know literally only two people who use it. They only use WhatsApp because they have friends outside Europe.
I think we need to think in terms of single countries when talking messaging apps. Again take WhatsApp. Pretty big in Germany and Spain, but almost non-existing in Denmark (who instead rely more on Facebook Messenger or iMessage).
Want to get a delivery? You'll be told about it via WhatsApp. Want to order food online? WhatsApp. Want to pick up your laundry? WhatsApp. etc. It's everywhere here and totally dominant. Deciding not to use it would make your life significantly harder.
Now I've got so many messaging apps. I just want one. Only one.
(based in the UK)
People who do have WhatsApp, probably have it, because most of the people they know have it.
Cause what parent described is common in EU + LATAM