Now I know you are not serious. There are no major metro areas on 81 besides possibly Harrisburg PA which generate a major rush hour on 81. Thus would your proposed passenger route get any significant number of people from where they are to where they want to go at a time useful to them?
You are correct; the traffic is NOT daily commuter traffic. But it IS heavy. There is an existing, new Amtrak train extension from Lynchburg to DC which greatly exceeded ridership projections. But it leaves prepostrously early in the morning from Lynchburg.
Roanoke is TWICE the size of Harrisburg. Blacksburg is also the size of Harrisburg, and would provide transportation between Virginia Tech and Liberty on one side, and the DC metro area from which so many of their students come from, on the other. Bristol would connect the DC area to the Eastern Tennessee area, where Eastern Tennessee is where almost 2 million people live.