A major concern raised in the article is along the lines of "passkeys have technical mechanisms that may disallow use in future".

That ... doesn't seem like a concern unique to passkeys, though?

It seems more like a policy rather than a technical aspect.

e.g. A website might decide they will only provide services if you upload a photo of government ID, or pass a verification where you show your face.

If it's software running on someone else's computer, you don't get full control regardless.