The Canadians privatized air traffic control. The airlines pay for it. Similar has been proposed here, even before Trump, but so far a suitable arrangement has not been made. In part because the non-commercial aircraft owners have a hissy fit about the airlines owning the ATC system and pricing them out. So far, that doesn't seem to have happened in Canada, but they had less private air traffic than we do anyway. BTW, in the US it's not paid for directly from the General Fund; there are airline and other user fees that cover most of the cost.

As you say, this is the air traffic equivalent of the federal government building, owning, and operating all of the railroad signaling systems in the US. Probably not the dispatching, but there could be a change in how some dispatching and maintenance functions are carried out.

The more direct comparison is with the federal and state/local governments owning and operating all the roads, with taxed private operators of the vehicles covering their own operating cost. Of course, the tax (user fee) doesn't cover the entire cost, but there's a contribution.