@mattab I figured it may be better to use a different userId hash per site.
Eg when many websites are tracked on the same Matomo, for example in an agency, then the same userId would always have a different hash per site which may be better and further anonymize the data.
On the other side it is maybe wanted to have the same userId across sites but then they could still not use this feature and "pseudo" anonymize the userId themselves.
I have no preference whether it gets merged or not.
I think if we consider that we are transparent about pseudo anonymising (which we are now), then we likely don't need to do more work to make it less easy to guess the User ID.
It would more important to let data subject export work with the Hashed user id see: https://github.com/matomo-org/matomo/issues/12839 (If we made the User ID hash different for each website ID, it makes it a bit more tricky (although still do-able), to export the data subject data across all websites.)
Sweet, I close it then. Re #12839 I left comment and don't think this should work. Before that you should rather remove the feature!