That doesn't make sense, and nor does the point
@Parmandur made re: Saltmarsh.
Why?
Because Winninger didn't call the Ravenloft book a "revisit", but rather one of the "Classic" settings they were bringing back. So GH may yet reappear, because TSR and WotC have both shown a totally irrational obsession with making Greyhawk happen over the last 30 years, despite the fact that every single attempt (no exceptions) has proven a failure, but it will be as one of the "Classic" settings.
It's clear Winninger sees essentially four categories of setting book: Classic setting, Revisit to existing 5E setting, New setting (MtG-based), and New setting (non-MtG-based). GH would be the first, just as Ravenloft was.
I've had more than one player ask why there isn't a Feywild setting book, or at least a book full of information/art about it, so that would make a lot of sense.