I believe the actual text of .2 says something close to "single-ply polyester woven sailcloth"
So Pentex (a polyester) is legan in a main, as long as its a woven cloth. No 3DL, NuClear, or similar construction.
In the #1, kevlar is not legal, but again Pentex is. I believe there are North 3DLs with Pentex. I do not know about Quantum Fusion.
Yes, anything goes in a #3.
Yes, there is a non-nylon cloth. .6 Polyester was often used as a replacement for 3/4 oz. nylon in PHRF fleets. It has never been legal in the
J/30 Class. I don't remember exactly which AirX fabrics meet class specs, but it is possible to get one that's too light. So you do have to be careful.