Can't know for sure obviously, but I would be surprised if emulators are allowed to use just-in-time (JIT) compilation techniques, as that's currently only allowed for Safari.Wow. This is the biggest reason I want to sideload. If this is for real and not still restricted somehow, this will be big!
Without it emulators will probably be pretty low in performance unfortunately. Could probably work for old-school consoles like NES/SNES/MegaDrive/GameBoy/etc, but I doubt anything 3D will work well without it.