Which just sort of loops back to how if Web-based chat had a spec with meaningful user traction we wouldn't have any real use for RCS in the first place.
Also how XMPP could have been that spec, if Google hadn't decided when launching (the first version of) Hangouts to go full Ayn Rand while doing it.
Which basically means, instead of having a federated mess as designed to replace the federated mess of SMS and MMS, we'll get a Google mess, maybe. But if Google was any good at making messenger apps, maybe enough people would use one of them that it wouldn't be killed.