Wrong. I am sorry for my previous words but you are wrong. I assume you don‘t understand how all of this works or tie’s together, let me help you:I am neither scared, uncertain, or doubtful but sure. Whatever floats your goat. They might roll out their own hub, there's no info on that. All we have is that they're implementing RCS UP and not Jibe late next year. Which, right now, only means an additional protocol like SMS and MMS. Which if that's all they do, will absolutely require carrier side support per GMSA and RCS standards. I don't have to know how it works, I only need to know what the people who control it says on how it works. They say it has to be implemented on your device and your carrier has to implement it. One or the other and it doesn't work. Just like SMS and MMS.
your misunderstanding seems to stem from you thinking UP is the counterpart to Jibe (Jibe is a service provided by Google). UP is nothing more than a PDF file that outlines how *one* (I highlight this for a reason, explanation follows) has to implement RCS so that *others* can interoperate with your hub.
Let‘s get an easy example going:
RCS requires me to say A and you understanding A, so that we can both do B. That‘s essentially what the UP file tells someone who‘s interested in providing a RCS hub for someone (or their own client).
The UP file being the guideline can be implemented by anyone, even you and me, if we have the resources and reach that Google or Apple does. Reach as in: I can pour resources into creating an UP compliant RCS service, that‘s capable of interconnecting with other hubs, but I need them to take me seriously and actually interconnect.
I‘m not sure if I‘m allowed to link this here, but this is the latest version of UP: https://www.gsma.com/futurenetworks/wp-content/uploads/2019/10/RCC.71-v2.4.pdf
As you can see, the only time carriers are mentioned is when it comes to billing for things.
Furthermore, the official website outlines the different roles and keyplayers (many being device manufacturers or third parties, unrelated to carriers): https://www.gsma.com/futurenetworks/rcs/the-rcs-ecosystem/
Hope this helps clear up any confusion.