Once we begin to move into space, traffic will be a two way street. Large human tended cargos will need to be carried into orbit as well as brought back down. Without a shuttle, how would the Hubble be brought back down after it's retired? Maybe they could redesign the shuttle with a smaller maximum lifting capability, and use the weight savings to make it more rugged and durable.

Another idea would be if the solid rocket boosters were built where they didn't have to be shipped through mountain tunnels. Then their size (and power) could be increased. Those allowing for a heavier more robust orbiter.