I don't see this going well at all. If Apple will not provide a Google Jibe-like backend service, it will be a scattered service throughout the world. Many carriers won't care at all to implement an RCS server, as that creates costs.
I work for a carrier myself. I'm not in the team taking care of mobile backend services, and I will sure ask them for some insights, but if there's no money to be made out of this, hardly any carriers will implement it, that's for sure. Leaving the Apple RCS implementation useless.
So I really wonder if Apple will provide their own backend service as a fallback like Google does, or not. Anything else would be ridiculous.
Apple has no reason to support RCS any further by investing in their own RCS hub. They tell carriers to do their job or redirect traffic to Jibe, most will probably do that one day.
More likely this bad experience will just cause iPhone users to have to leave MVNOs like Mint and Visible for more pricey plans. Apple has never been good about supporting US carriers outside of the big 3. You can't use an MVNO on an iPad or Apple Watch. You can't do the iPhone upgrade program either. And you usually can't do eSIM during setup or transfer your eSIM.
That‘s not on Apple. MVNOs run on the big networks (the ones that currently support RCS). Most big providers that rent their infrastructure to smaller ones purposely gimp what functionality MVNOs can offer.
In germany there are essentially 3 big carriers with their own infrastructure, with a plethora of smaller ones that simply "rent out space" on the big 3 infrastructures. There are also many who simply resell big 3 contracts. Almost all of them are gimped in one way or the other (loads of then get a fraction of the bandwidth / speed you can get on these networks, loads of them didn‘t even have 5G until a year or so ago when the big carriers started giving that to smaller ones on their networks).
I had a Telekom contract (a full one) via a reseller once years ago, it was literally the same contract and feature set you could get straight from Telekom for half the price… but it was gimped in certain ways (like eSim transfer during setup -> it was disabled for my contract due to Telekom not allowing resellers to have these useful features).
TL/DR: you‘re pointing your finger the wrong way, these carriers hold back the others on their networks.