Google seems to be preparing to migrate Google Search Console from /webmasters to /search-console URLs. This is about a year after Google rebranded Google Webmaster Tools to the Google Search Console.
Dan Shure posted several screen shots on Twitter of the new URL format.
Here is a picture of him accessing https://search.google.com/search-console/mobile-friendly:
When I try to access it, I get this coming soon page:
But he gets a real new mobile-friendly testing page:
He did say he is part of a beta, but when he got a notification via the Google Search Console, the link in the notification took him to this new URL.
I assume Google has been planning the migration from /webmasters to /search-console for some time, and the best way to make sure the migration goes well is to beta test it with some users.
Postscript: Google’s John Mueller has confirmed Google is testing a new mobile friendly testing tools.