One of the problems with the Shuttle was that it was intended to do everything - heavy lift, orbital operations, satellite servicing, etc. As a result, it's pretty huge and very complicated. Aerospace vehicles cost by the pound and weight snowballs quickly. Before rushing into a 2nd generation shuttle, perhaps we need to step back and determine what we want the vehicle to accomplish.

Do we really want it to be our heavy lift booster? I don't think so. You don't need a crewed vehicle to launch a satellite. You can do that a lot cheaper with an expendable booster like the Delta IV. Getting rid of the requirement to carry huge payloads would dramatically reduce the size and cost of the vehicle.

Perhaps all we need for a next generation shuttle is the ability to carry a number of passengers (say 7-10) into different orbits with a relatively modest payload, say 10,000 pounds. This would allow carrying a replacement crew to the ISS with a good logistics supply and returning stuff to the ground. It would also allow for other missions. Let outsized payloads be launched on existing boosters and reserve the new shuttle for missions that require humans.

I fully agree with you that the new shuttle should incorporate new technologies to increase reliability, reduce labor for mission turnaround, and increase safety.

My approach could well reduce orbiter from a vehicle about the size of a DC-9 (MD-80) airliner with an empty weight of around 180,000 pounds to perhaps a vehicle about the size and weight of a Gulfstream IV business jet. In turn, this would greatly reduce the amount of energy needed to put it in orbit, perhaps by as much as 75%. Remember, it takes propellant to accelerate propellant.