For Duke, most feedback on the compiler specification has been listed in https://git.m-labs.hk/M-Labs/nac3-spec/issues/6. Besides that, we remain interested in keeping the spec simulation friendly, feedback here https://git.m-labs.hk/M-Labs/nac3-spec/issues/7 .
At this moment, we do not use kernel from string. I think modifying kernel invariants in host only code, as discussed here https://git.m-labs.hk/M-Labs/nac3-spec/issues/5 , is one of our main ways to dynamically get kernels prepared before compilation.