One issue with Google's RCS implementation is that they've added root detection, something mandatory if you follow the RCS payments spec. Google will probably eventually want to mirror Apple's "send money*" feature to their messenger which precludes GrapheneOS and other non-official software (including Google's GSI images).

*: unless someone does a chargeback after, which makes the money disappear from your account, a major source of "oops I accidentally sent (too much) money (to the wrong person)" scams