I think those are all very impressive guesses, forgive me if I make a few objections.

Shinsou's quirk is probably based on pheromones, similar to the purple man in Jessica Jones if I'd have to guess.

However, it was said it is necessary for the opponent to reply for the Quirk to activate, and I don't think Izuku held his breath. Moreover, he was able to use it on Deku after the match when there was a considerable distance between them. The fact it activates only when Shinsou wishes it also implies it is not an indiscriminate attack.

Aizawa has floating hair when he uses his quirk. So I'm guessing he emits some sort of radiation that blocks enzymes from catalyzing

It's quite odd it would affect all Transformation and Emission Quirks though, seeing how each ability differs from all others, without influencing Mutation Quirks.

Fumikage is a hard one. If I had to guess scientifically, he's probably a conjoined twin with dark shadow.

It's still a mystery how Dark Shadow would be able to increase its mass with darkness, though, and how it occupies no space under Fumikage's clothes.