The only thing I might add is that although it’s true that LINK has surface stations, there are fairly high walls at every point except the on-ramps at the ends and (of course) the tracks themselves. While those obstacles aren’t insurmountable, they aren’t any easier to negotiate than simply jumping the turnstile. In any case, you’d have to have security, so the surface station issue isn’t really relevant.
You couldn’t have turnstiles in the DSTT when shared with buses, of course, but it’d be easy enough to assume anyone exiting without an entry swipe is coming from there and assess the maximum fare.
All that said, despite my East Coast biases I’m not terribly energized on this issue and am happy to see how the honor system works out here.