I think you will see more of this class of attack.

Lots of companies have various 'forgot my username'/'forgot my password'/'trying to sign up for a new account with a new email address but existing phone number'/'add a friend by email or phone' flows. It's very easy to accidentally leak some info that shouldn't be leaked while implementing such a flow, since you are peering into the users database querying by email/phone/other identifier while the user hasn't properly authenticated yet.