-- consider as in a counterargument that they're going to make a proprietary linux?

You have to be careful with in-house developed tools though. Canonical outright owns the majority of the code and outside contributors need to sign a contributor's licensing agreement that would allow Canonical to use their code in a proprietary version if Canonical chose to do so.

Yes, the GPL version would still exist, but Canonical could continue working on the proprietary version and not push the commits to the GPL version.

I'm not saying Canonical would do this. And you can replace "Canonical" in the prior sentences with any company and/or software that requires a contributor licensing agreement.