That mock-up was made by a redditor, way back before we even know it was called Shadowbringers - I believe he used 'Violettide' as a working title for the mock-up, and after FanFest, he updated his mock-up with the revealed logo. So no inside-information going on. Apparently, now it's also a video.
Would love to credit the guy, but I can't remember his reddit username...