Re: Yeah, no
There's lots of confusion about the implications of a right to "derivative" works in the (US) copyright sense both in this post and the article.
In your comment above it's not clear whether you're saying QDOS and 86-DOS are both "derivatives," but let's be very clear that the "_design_" bit doesn't fit US copyright. Copyright protects original* expression not design or function. Design and function are the domain of patent law.
Neither QDOS or 86-DOS would be a "derivative" within the meaning of the copyright law if they were just functionally "compatible" systems based on manuals (i.e., information about their design) because the particular way they were expressed (i.e., literally written) was not copied.
More fundamentally, the article is misleading because an infringing* derivative work isn't forfeited entirely to the copyright holder. For example, the rights to prepare* and distribute* derivative works are separate from the rights about actual copying. A derivative work will typically have material owned by the underlying work's copyright holder and, separately, material that's still owned by the derivative work's author (namely, the original* and protectable* expression that the derivative work author added). You always have to think about those rights and their remedies separately, because that's how copyright works--it's not a single unitary "copyright" but a bundle of rights.
The underlying work's copyright holder remedy is _not_ any sort of automatic right to the infringing derivative work's protected expression. And infringing derivative works aren't punished by making them public domain. (In general, copyright law is not meant to be punitive, even if that's sometimes the result.)
* indicates legal jargon; like the word "derivative" they indicate legal conclusions that can't be reached until various requirements, doctrines, and exceptions have been applied. As with the word "derivative," it would be a serious mistake to assume their meaning is obvious without an understanding of copyright law.
Disclaimer: I happen to be a lawyer, but this is just my personal opinion. It's not legal advice and should not be relied on for any purpose. You shouldn't believe anything you read online, anyway.