Magnus Carlsen against 10 blindfolded. Timur Gareev plays 30 players blindfolded. I was wondering if these super grandmasters all can at least play 7 masters blindfolded and beat them.
This is more a comment than an answer.
The attached fragment is Mikhail Tal commenting his blindfold simul against 10 first category (approximately 1800-2000 Elo) players - as the match goes, board by board. The fragment is a part of 1968 documentary on limits of human mental abilities.
The movie is in Russian; if there is an interest, I may try to translate.
The answer to the headline is definitely "yes". I would be very surprised if there is a top player who is unable to play 10 blindfold games.
Playing seven masters and beating (all of) them is a different issue. Remember that Kasparov limits the rating of his opponents at simultaneous exhibitions to under 2000 Elo. Of course he can beat much stronger players simultaneously, but it increasingly becomes a question of energy and concentration, not so much pure chess class.
This is even more of an issue in blindfold chess. If we talk about US master titles (I think they roughly start at 2000+ Elo aka 2100 USCF rating), I think it already becomes quite hard to get a 100% score in seven simultaneous blindfold games. But I still believe a top grandmaster would score highly. If we talk about real masters, i.e. IMs, GMs, I think even top grandmasters would struggle to score more than 50%.
Paul Morphy once played a blindfold simultaneous against the 8 strongest players of Paris and score 7/8. Maybe that's comparable to top player against lower masters.