I have a fairly mild case of Avoidant/Restrictive Food Intake Disorder (ARFID), and I wound up at one of these places with co-workers in San Francisco one time. This is basically a nightmare scenario for me. I'm socially expected to eat, and I'm presented with strange dishes and lots of unwanted attention when I inevitably don't eat.
But we spoke with the server, and she found me a dish from the prix fixe arrangement that I could eat, and spent the night just making sure there was always some of that dish on the table.
Everything went better than expected. Sure, I don't have to be worried about death from being exposed to food I won't eat, but I could've called ahead, and would've, if the stakes were that high.
I guess all that's to say: good restaurants are pretty accommodating, even when they aren't doing the normal menu thing. It's really not that crazy.