As much as I hate the E145, IAH-ISN appears to be an appropriate market for it. Forget about CASM, I'd like to see the RASM on that!
Other than the CRJ, which imo is worse, I cannot think of another suitable aircraft short of connecting through somewhere else.
If UA continues to develop new markets with the E175, I will consider that as a Change That I Like. But really, they've also got to improve the soft product.