^ The F-1B's haven't been decided on. It's just an option that a contractor is bidding.
I agree that NASA should move away from the RS-25E's, which despite modifications for expendability are still too expensive for anyone other than NASA. The RS-68's aren't that much better, especially given their much lower ISP.
They should probably start pursuing the recent innovation of using a swirling oxygen counterflow (injected upward from near the throat to swirl around the sides of the combustion chamber, providing cooling without built in passages).