but what about reimplementing a compiler from scratch without reusing any of Apple's code? It wouldn't fall under a definition of Derivative Work under terms of Apache 2.0 then
Apache license don’t say anything about clean room reimplementation under other licence because it’s a tricky subject beyond the scope of the license. I personally think that if someone reimplement Swift, name it Schwift, guarantee it’s 200% faster (for some reasons), and then sell commercial licence of that it should be sued (but with such business plan I believe he’ll go bankrupt first).
Apple logically won’t comment on what they will do in case of a "clean room" implementation because they have zero interest in anybody doing such a thing.
And actually nobody have any interest in such a monstrosity (except maybe for theological reasons?). The project is goddam Appache2, fork it if you want, but spending any second trying to reimplement years of works is a total waste of time. Want to start something from scratch? Fine but do something original. Want to improve swift ecosystem ? Fine but work on the main project or on a clean fork!
Also, I'm convinced that many many people do have interest in this. Many people were interested in GCC existing in parallel with whatever other compilers were available. Heck, Chris Lattner's Clang wouldn't exist if C and C++ were "protected with patents from patent trolls". Are you saying that all these alternative compilers were a total waste of time?
Should? What rule, law, or moral code does it break to reimplement something?
Like you, I would have a pretty hard time being convinced that this was actually a good idea, though.