Which is why they are treated as if they are cookies and are cleared any time the cache or cookies are cleared so that they can not provide an additional tracking vector beyond what cookies can do (and when 3rd party cookies are partitioned by site/frame, they are also partitioned the same).

There are LOTS of privacy teams within the respective companies, W3C and IETF that have looked it over to make sure that it does not open any new abuse vectors. It's worth noting that Google, Mozilla and Apple are all supportive of the spec and have all been involved over the last year.