The GH mapping project is amazing.. and slightly odd given the lack of any ongoing materials from Wizards.
[Although there are clear guidance on how to use most stuff in GH and other settings.]
However it is clear that there is a clear wish to bring back GH, but in a way that is distinctly different and unique.
There is an excellent 5e GH conversion out there.. by no other than .. well maybe .. not.. Chris Perkins*
I am an innocent abroad when it comes to Greyhawk bad old grognard gatekeeping, it just goes to show the channel bubbles you can be in. I suppose you have to ask whether you let them own it and spoil it for you?
I've met some nice Greyhawkers so far who are very open and weren't fussed what you were using to run games with in Greyhawk. I continue to warm to the notion of a game, possibly even doing T1-4 to get things going. It'd be a streamer I think.
Anna B. Meyer has done a further Greyhawk map at the latter part of the timeline and is planning a further one next year. The maps and history are drawing me in. There are probably a few modules I'd want to use, and some of the Living Greyhawk material as well.
I'd probably use Blade & Spell as I want to explore a range of things and use the game as an ongoing and iterative development of the game.