A practical approach would be: No set cast. Let's explore this new universe Abrams helped to re-energize. Each episode could have a different setting. One could be all Klingon, one all Romulan, or even all Tholian. Or you could even set it in Starfleet Academy, or Starfleet Command. Command is monitoring the situation of a starship, and we get to see what space combat is like on the other side of those communcations to Starfleet. Kind of like 24 meets Star Trek. Each story, however, affects the universe. A Ship explodes, and three stories in, the characters could be discussing that situation. We could even go back to the new movie cast once in a while, and see whats been happening with the characters. The finale of the show could have the Enterprise going in for re-fit prior to TMP.