Maybe this is a bad idea, but... What if, instead of the current way where every call (including native stuff) is sync by default, it were the other way around?

Maybe this is a bad idea, but... What if, instead of the current way where every call (including native stuff) is sync by default, it were the other way around? You'd quickly whitelist basic things like arithmetic and data struct access as sync, then you could maybe detect other things that should be sync if the event loop is spinning suspiciously fast.