According to my armchair unlicensed psychiatry, Musk would absolutely flip the “on” switch on the Borg.

The main reason is that I think he wants to be remembered more than anything. He’s realized he won’t have time to find immortality or load himself into a computer, so having people speak his name and see his face for centuries is the next best thing. Does not matter if it’s for bad reasons.

He has also talked about the importance of preserving the light of consciousness. The Borg are perfect for this.

And then in general, he seems to be on the extra-sociopathic end of the tech bro spectrum, where the point of a life well lived is productivity and accumulation of assets, and emotions are a weakness. He would probably get all hot and bothered at the idea of being able to assimilate all life forms, share their useful technical knowledge across the collective, and summarily discard all the cultural distractions from the Great Productive Mission.