I cannot decide if LLMs would be excellent at writing in pure binary (why waste all that context on superfluous variable names and function symbols) or be absolutely awful at writing pure binary (would get hopelessly lost without the huge diversification of tokens).

Binary is wayyy less information dense than normal code, so it wouldn't work well at all.

We would still need the language to be human readable, but it could be very dense. They could build the ultimate std lib, that goes directly to kernels, so a call like spawn is all the tokens it needs to start a co routine for example.