It's amazing the results you get from treating your users like competent human beings rather than idiot cattle.
All this snark just to dodge obvious questions about your approach?
Speculation on the potential scalability of this approach seems absurd given that membership numbers have been successfully used by organisations of every scale for centuries.
The concern is not with the scale of the organization, but with the number of organizations a user is a member of, which has exploded since website accounts appeared.
While I don't disagree that there's a lot of useless account creation, I'm still member of at least magnitude more of useful online accounts that I or my parents ever were offline.
I know that whenever I have to contact a service for which I only have a long numeric number I have some reference handy to make sure that I don't fuck it up.
Right, sure.
And how often do they forget their numbers (rather than getting them wrong)?