Agreed. However, Widevine is Google's thing and it's plausible that they'd ship it with some non-free build of Chrome. Unless they're worried about trusting the OS, in which case my original argument is void.

Plausible sure. anyone using any other plugin is also plausible, though much less likely.

The point is since it's not standard Linux and BSD will get the shaft.

Wildvine works on Linux today.

And other plugins that other providers might choose to use?

In most browsers, they aren't actually plugins in the typical sense. As far as I'm aware, Chrome doesn't allow any other EME modules to be installed, so if a provider wants to work with Chrome they must support Widevine.