for what use is meta-ethics if no ethics results, or at least, practical procedures for discovering ethics?

We have the processing unit called "brain" which does contain our understanding of the human context and therefore can plug a context parameter into a metaethical philosophy and thus derive an ethic. But we can't currently express the functioning of the brain as theorems and proofs -- our understanding of its working is far fuzzier than that.

I expect that the use of metaethic in AI development would similarly be so that the AI has something to plug its understanding of the human context into.