Yes, RCS is dead. Google’s RCS is “just another app” and just distracts from the fact that the carriers (which had implemented SMS BEFORE Apple’s iPhone even existed) need to go back to the drawing board and come up with the replacement.
If I may add to this, even if Apple were to gain access to Google Messages’ RCS API, it wouldn’t truly be interoperable. As a matter of fact, it would just further solidify the smartphone duopoly, as you would either need an iPhone or an Android phone blessed by Google to have better texting than MMS. Feature phones? Nope. Cheap Android phones without the Google Play store? Nope. Desktop computers, tablets, smartwatches, VR headsets, SIM-less device classes we haven’t even come up with yet? Nope*. Edit: Oh, and it would likely kinda suck for multi-SIM phones (oh, like most recent iPhones released in the past 3 years…) when used on the second SIM (imagine not getting your texts because you’re abroad and on the second SIM’s network).
Any new standard should be 1) interoperable, 2) if compatible over the network should also be equally compatible with standard Internet routing (so multidevice sync can be a thing), and 3) should not be tied to a subscriber number, even if it’s a carrier led initiative (which it should be for compatibility with non-smartphone phones). Alas, no one’s interests really align with this goal, except perhaps the users’. The carriers don’t want to be dumb data pipes, Google doesn’t want interoperability with non-Android and non-iPhone devices (even the iPad**), and Apple wants to promote its ecosystem (and iMessage is really the only system in use, other than maybe Facebook Messenger, that doesn’t suck at multi-device support).
* Well, it’s a Nope for SIM-less devices, but also a “no sync for you” scenario for any SIM based devices, as Google Messages’ phone+tablet syncing support is utter garbage (for the same reason Google Allo, Google Duo, and the new Google Pay were all duds and why WhatsApp still doesn’t have great multi device support, using phone number as primary identity, even if the service isn’t locked to that specific SIM, is a terrible idea these days).
** RCS doesn’t really make sense in iMessage because you’d have similar issues with RCS and multiple devices as you do SMS. If you own an iPad, a Mac, and an Apple Watch, RCS is kind of a raw deal for you, especially if we get stuck using Google’s gateway and Google is the one writing the code. Apple had to jump through a lot of hoops to get SMS working through the Continuity features, and Google has proven that it can’t do multiple device support anywhere near as well (especially considering that Google Messages uses phone numbers for identity instead of account based identity, which is what Apple does).