Some years ago I worked on a system let banks do identity assertions with proofs via SAML attributes instead of sharing customer PII. It is now a federation of banks in wide use for govt services in Canada. The use cases were really limited because the federation partners were too conservative to extend the identity services to relying party consumer applications real people actually wanted to use, and institutional sales cycles meant product feedback was glacial, so it has existed for over a decade in this relative backwater of gov-tech. I think identity companies have mostly failed to get traction because of a terminal lack of consumer sexiness, whereas Stripe has the jelly.
Other companies in the identity space have been working on protocols and platforms, but none of them had a user base to extend an identity federation services into, which means they have never been able to make a real or viable product, just interesting techs. An internet payment provider with young consumer traction getting into identity is a Very Big Deal.
It's going to position Stripe to knock out a lot of retail banks who can't offer similar services. Imo, this could make them bigger than Apple.