There's a way to request special meals at booking? Is it a thing where you choose among the handful of available types of special meals, or a write-in field? (If a write-in field, I'd worry that they won't read it until it's too late, and won't get you the right type of meal. I've always called AA on the phone to request a special meal.)

AA doesn't have special meals for every food intolerance. (My niece is allergic to citrus, and there's no "guaranteed-citrus-free" special meal.) They just have a handful of "catch-call" special meals. That's why a conversation with an AA agent may be necessary to figure out which kind of special meal would work best for you.

As to the SWU, I don't know whether it affects your upgrade chances. If you do get upgraded at the last minute, you might get asked by the FA whether you want to your special meal from the original cabin or a regular meal from your new cabin.