I don't think Turbolinks is a good idea from a usability standpoint. Too many UIs have a similar bar at the top, and they mean different things: a browser's loading bar, a website's loading bar, a website's read-progress, etc. I think it increases the user's cognitive load (at least for this user) to figure out which kind of bar it is and why the top of the page is animating.

Turbolinks also makes websites appear extremely slow when on slow connections. It's much more frustrating to sit there with a loading bar hovering at 20-30% than to see a spinner.