Derivative works aren't some unknowable arcane legal term. They're a pretty fundamental aspect of copyright law. The canonical examples of derivative works are things like adaptation of a book to a film, translation of a book, or a sequel.

And given these examples, it's very clear that recompilation to play on modern hardware is quite similar in spirit to translating a book into a different language, which makes it a derivative work. The other alternative is that there is insufficient creativity in the recompilation effort to merit independent copyright at all, in which case it's just plain copying of the original work. In either case, it's infringement.

So, wishful thinking it is.

There is a bazillion of jurisprudence about decompilation in the EU . Just search for your favorite case. I'm based in the EU (France). But FYI, despite what you may think, in practice the US is more lax about this than the EU is.

In the EU, for example, decompilation even if you don't distribute may very well be illegal (because it would be an unauthorized temporary copy of the program); the US courts are way more lax when it comes to these temporary never-distributed copies (which are almost always fair use, a concept that doesn't exist per-se in the EU). This is a big problem in the EU for security research (which obviously does not fall into interoperability).

Emulation would be acceptable, which is yet another reason the interoperability clause does not apply (since you _already_ have a way to interoperate that doesn't require distributing copyrighted software, and the EU interoperability clause very explicitly says that then it does _not_ apply).