I've implemented it into a few services, but they were relatively low-risk in terms of the information retained. In fact, for most services it is possible to u

I've implemented it into a few services, but they were relatively low-risk in terms of the information retained. In fact, for most services it is possible to use password resets for just this purpose. Sign up with your email and an incredibly strong password that you never retain, reuse or remember. Next time you need to log in, just reset your password. Same thing. By offering passwordless login from the outset, you make doing so easier. The one pain point is the need for the user to have access to their email, which these days is pretty easy.