[dnautics]

it's not really a generalizable solution, though, because suppose you need an unnatural AA that needs a specialized ribosomal cavity and that cavity hasn't been developed yet. And you need the material by a year's time. You are not going to evolve a ribosome to make your peptide. And, there are post-translational modifications that are too big to fit into ANY cavity, though in theory you could use tricksy chemistry to figure out a downstream processing step, that chemistry may not exist yet, or it may require a pure enzyme that is a pain in the ass to obtain, etc. etc. Finally, charging the correct tRNA is not necessarily easy or efficient.

Unlike well-designed programming architectures, biology is usually not "trivially composable". Oddly, SPPS is. Yes, there are corner cases, but those are more the exception than the rule.