And (probably) final update in this thread: PC Gamer have updated their article after talking to an IP lawyer:

> "I would characterize this NOT as a DMCA take down notice and instead as a warning shot that the software, Dolphin, if released on Steam would (in Nintendo’s view) violate the DMCA," says attorney Kellen Voyer of Voyer Law, which specializes in intellectual property and technology law.

Looks like at least one lawyer shares my analysis :-)