All I see is billions of views being taken away from FB/YouTube and others...and this is the great danger.
Google, FB, and any gaming or streaming service is losing their prime demographic: teens.
During the next major password dump, acquire the master list.
usernames.com can be a freeview model site where you display all of the 'acquired' usernames much like how RetailMeNot displays coupon codes. Click on a username and have the availability to purchase the password.