Eventually the current generation of shuttles will be retired.
Designed to carry crew and cargo, the existing orbiter is complicated because of it's dual role of crew transport and cargo transport.
As an alternative, the next generation shuttle should be a smaller reentry vehicle designed only to carry the crew. The job of launching cargo should be assigned to an unmanned heavy-lifter similar to that used by the Russians to resupply their Mir space station. Both vehicles would be recoverable. The main advantage of this design is enhanced crew safety as their launch vehicle would require less energy.
NASA: Are you listening?