We don’t know any details. Google is trumpeting a success and indicating a willingness to assist but it doesn’t really tell us much of what it will look like. Apple is committing to RCS, the industry standard as it is (and I assume will be as I hope it breathes new life into the standard…) and not Google’s current RCS + proprietary bits implementation.
When MS created a Windows Phone YouTube app, Google blocked it with requirements that were either arbitrary (it needs to be HTML5 for example despite iOS and Android apps being native) or impossible to meet. (requiring specific access that Google would not provide)
So while Google framed it as “Microsoft just needs to do X, Y, Z and it’ll be all good!” - sounds good but it intentionally made said requirements impractical or impossible to complete.
Since Google’s been conflating their RCS implementation with RCS the standard, I think it’ll be a funny (if unfortunate) monkey’s-paw result if Apple’s adopts RCS completely as the backup to iMessage but continued carrier and Google implementation fumbling results in no change and the iPhone having to resort to SMS/MMS anyway.
(see: a while back when AT&T’s RCS could only be used between a couple AT&T Samsung phones - but I do hope it’s different this time, I got a group chat I rather take off Instagram.)
There is RCS the standard, which isn’t really used - maybe Apple’s support will give it a boost. Then there is RCS + proprietary addons that is used, Google iMessage.