That statement means the comittee does not want to stop it from being developed. The question is, has it? They mean a specific implementation could work as portable assembler, mirroring djb's request for an 'unsurprising' C compiler. Another interpretation would be in the context of CompCert, which has been developed to achieve semantic preservation between assembly and its source. Interestingly this of course hints at verifying an assembled snippet coming from some other source as well. Then that alternate source for the critical functions frees the rest of compiler internals from the problems of preserving constant-timeness and leakfreedom through their passes.
C already existed prior to the ANSI standardization process, so there was nothing "to be developed", though a few changes were made to the language, in particular function prototypes.
C was being used in this fashion, and the ANSI standards committee made it clear that it wanted the standard to maintain that use-case.
