I haven't encountered any difficulties with the GIL either, but that doesn't mean it's not a problem.
I really do hope Gross is successful. It does seem like he's "got an angle", so to speak, on the problem. At the very least, he's coming into it well-informed with his eyes open. He wants to try excising the GIL (and FB is apparently footing the bill to boot) so it's stupid to object, eh? Who cares if he wastes his time? He's not hurting anything. And maybe the horse will learn to sing. :)
The FUD comments came when I was on my phone and in https://xkcd.com/386/ mode. I was just disappointed seeing so many comments that were, well, FUD. FUD may be terse, but I don't think it's strong language.
There's a lot of misunderstanding around the GIL in general.
I too hope he is successful.
I read the document. Sam Gross seems to have a clear grasp on the risks associated with this kind of project (I would quote the relevant part, but google docs is a clown shoe.)
One the one hand I wish him luck. If he pulls it off he'll be a hero. On the other hand this seems like a huge "turd polishing" for a problem that one only encounters if one is doing something ill-advised. The GIL just isn't that big of a problem in practice. I've been writing Python for going on twenty years without ever encountering a single problem due to the GIL.