It feels like it might be some sort of crime specifically to misrepresent your product as being capable of X and sell it to people who you know will try to use it for X, when X is disallowed by the ToS of the platform. Con-artistry of a sort.

You could see that as "false advertising", but considering they link to the Apple TOS they're not really hiding everything.

And actually, merely adding features doesn't seem to be forbidden as long as the features you add are not "inconsistent with the intended and advertised purpose of the Application as submitted to the App Store"

So let's say you release a file manager and later, surprise! It's also a SNES emulator! Well, then yes, I can see that against the TOS. But if you're just making improvements to your app, I don't see a problem.

I think illegal is the correct word there. I won't comment on the statutes (IANAL).

It was just a hypothetical though. AppHub has plenty of legit use cases under Apple rules, and it's probably not all that dangerous even if you "mis-use" it slightly. AppHub would have to explicitly encourage people to break the rule to run afoul, or Apple would have to organically notice a bunch of apps doing a bunch of outlandish feature flipping.

With the way the CFAA is enforced, you look at a computer in a way someone with money doesn't want you to and it's federal prison worthy. I'm sure an over eager DA could and would try and make the case.