Right now the thrust of NTRs remains quite small with higher density propellants, which may work for rockets where you're preserving the chamber pressure, but doesn't work for NTRs, where the constant is the power of the reactor. One of the great benefits of water-propelled NTRs as opposed to hydrogen-propelled is the much higher thrust-to-weight ratio, and it's also why methane is a fantastic compromise between efficiency and thrust.
Andrew and I have discussed this in the past in the engine update comments, but I'm making this an actual suggestion as well.