And PS Vue would only be of use in the US.

At the end of the day, PS Vue doesn’t offer anything compelling enough to acquire. A few subscribers and a bunch of licensing deals to broadcast TV over the Internet. Apple could get the same deals as Sony, Sling, Directv, Hulu, etc. Cable networks aren’t exactly being stingy about licensing.

There's no way that Apple would allow tvOS to run on unaudited hardware like the PS4.