At Friday April 6 all of a sudden the Twitter account of VMware Education sent Tweets about vSphere 6.7 linking to Youtube videos which seem to explain vSphere 6.7. Less than an hour later the Tweets and videos were deleted. Below you see a screenshot.
Someone at Reddit posted a comment the release is scheduled for April 18.
Rumours about vSphere 6.7 to be released in 2018 started in the beginning of 2018 when The Register published this article. It describes some of the supposed new features of the 6.7 version which does not seem to be very exciting.
Mind I am not part of the Beta program nor signed a NDA.