Only the GM is blindfolded.
Blindfold Chess Game against GMs

That's a fair handicap. Larry Christiansen has played blindfold simuls against 1800s-2000 rated players and usually wins. Not all 26xx rated GMs are that accomplished at blindfold though.
Still, I'd favor the GM. Blindfold takes about 500 pts off your rating.

GM Hammer from Norway (Thats 2700 rated GM i think) played 5 or 10 min blitz game blindfolded and he lost some games while streaming and talking.


On another note - I played a blitz match against FM Or Cohen some years ago (when I was 1900ish). He was playing blindfold and it ended 2.5:2.5. The games were interesting.
We played a real blitz match (he's rated 2350 FIDE more or less) last year, which ended +2 =2 -18...

Well, based on the results of the Melody Amber tournaments, the stronger the GM, the better they are at blindfold chess. Anand, Kramnik, Ivanchuk, Morozevich, Topalov and Aronian were repeat winners of the blindfold tournaments.
Carlsen didn't get to play in many, but he won in 2009.
So, in modern times, the best blindfold players also generally happen to be the best players.

The problem with an open tournament is that there are many people who claim to be able to play blindfold, but actually have real difficulties pulling it off. Viktor Korchnoi played in a couple Melody Ambers, but just couldn't cut it. He kept making illegal moves.
Blindfold chess is much more demanding on arbiters than regular chess. You probably will never see an open blindfold tournament.
In my experience, the best blindfold player I've seen in person is Larry Christiansen. I played him in an eight board blindfold simul against all players rated +2000. I think he broke even. I managed to win his "Storming the Barricades".
If a 2600 GM played a blindfold handicap chess game against 1800 - 2000 chess players one on one, who would win in a 30/30 game?