Gave this a quick spin this morning and appears to work great on standalone sites and multisite primary sites.

For subsites on multisite, if the user is the same as the primary site it fails to store the token (i presume due to one already existing but not linked to subsite).

Really looking forward to seeing where this goes as it's a great experience.

One thing to note, if you do not have a Nickname set in the user profile it displays the existing username on the login page.