I actually didn't believe it at first, but here is a press release he put out in January, about the reason he has decided to start work on 5th Edition material ahead of WotC making the setting available for commercial reuse:
The press release goes onto name a number of products that Greyhawk Grognard is working on. And he later posted about a playtesting program he is running to iron the bugs out of anything he is making. (The playtesting slots are all booked up, before you ask.Greyhawk Grognard blog wrote:BRW Games Greyhawk Product Announcements (sortakinda)
Going through the Great Greyhawk Survey really got me thinking about what might happen if my favorite RPG setting* is ever opened up in Wizards of the Coast's Dungeon Masters Guild. Specifically, there's a line in the FAQ that opens up the possibility:
So it's definitely possible, even likely (especially considering they brought Ravenloft into the fold), that Greyhawk will be an option someday. I have to reiterate that I have no idea when that will happen, or even if it ever will, but I am basing all this on the (admittedly speculative) idea that it will. Eventually. I'm guessing within two years, but it could be next week for all I know (in which case, boy am I behind schedule!).
- Q: Is this going to remain Forgotten Realms only, or are other settings/IPs to be considered in the future??
A: We intend to open up additional settings and IP as time goes on. However, for the time being, we will remain focused on the Forgotten Realms.
With all that said, here are the sortakinda product announcements, dependent entirely on whether or not WotC ever adds Greyhawk to the list of settings in the DMs Guild. Even if I just end up writing them for my own game, they'll get written.

What do you think of Greyhawk Grognard's gamble? How much content do you think he can make ready before any DMs Guild launch happens for Greyhawk?
Do you think he will be waiting a long time? I know that Spelljammer has been mentioned a lot recently, but are there really many other campaign settings that would stand in the way of Greyhawk?