I’m just sitting here frustrated because I’m wanting my family to move away from messaging me over SMS (they mainly use iOS), but they refuse to download any extra apps. But Google’s RCS really doesn’t look like a solution either since it mainly just seems to be a way of enforcing Android as an ecosystem, and they don’t even make RCS available for 3rd party apps to use either.
I think it’s complex and the problem have been many things. When Apple pitched an open version of iMessage to the carriers long ago they refused because the didn’t like the E2EE. They were surprised when Apple later introduced a proprietary version (and subsequently discovered it was a competitive advantage).
Now there’s a Client-server encrypted version of RCS in GSMA but the E2EE version is Google’s and running on Google’s service. It was only recently that two carriers in the US agreed to use Google’s messaging app for interoperability but is E2EE in GSMA?
Interoperability have been a problem as at one point carriers weren’t even interoperable while using Universal Profile (I think they are now). Apple surely wont use it unless forced (it makes business sense not to) but between GSMA Universal Profile (which Apple would have to use) and Google’s much better version based on the Signal protocol the current situation is also a mess.