I've been playing around with sql-sanitize for a while and I've found myself executing
UPDATE users SET init = mail; almost every time after --sanitize-email.
I'm aware that in some cases, like when you're using bakery, users.init doesn't contain an email address but I think it's the edge case and probably drush can provide a command modifier for such cases.
So should --sanitize-email modify users.init?
I think at least a mention to init field in the help/docs would be useful.