The messaging app front I consider to be a long-term stalemate, mainly due to crippling network effects. Another factor is that strange psychology at play when making app decisions, where a person will have page after page of junk apps on their phones, yet utterly balks at the notion of installing a second messenger.
Even if a large actor (say, the EU?) managed to bruteforce some interoperability into being, I wonder whether that would be to the detriment of small apps in terms of undermining (or even eliminating) their privacy protections. I can use the likes of Session or Simplex all day long, but if the other side of the conversation is on a corporate product like Whatsapp... It runs into the same problem as email.