Third party apps like Textra or Pulse can't access the RCS APIs, if you want to use a different carrier messaging app you can't use RCS currently. Also as far as I know the system doesn't actually know what RCS messages are and they're stored as SMS/MMS internally. Like if you restore from a backup or clear data on Google Messages, all your existing RCS messages appear as SMS/MMS.
Eh, maybe take this with a grain of salt - I cross posted this from !android@lemdro.id, but taking a closer look at the article their source is this tweet (nitter link), and the account directly says in the account bio "Not a Google Account, not affiliated with Google". So just be warned this is not an official announcement from the Pixel team like the article claims.
And it has a reasonable antenna and a proper amplifier. The kit to talk to the satellites isn't usually exactly like the kit to talk to cell phone towers. In theory you send and receive on the correct frequency and it just happens but usually you either need to be pushing a little bit more power or you need to be highly directional to get reliable communication.