Are you aware of Juliaberry (Julia on Raspberry Pi)?
I played with it a little bit. I could get very fast gpio bit banging speed (about 100 ns per ccall to libpigpio, so it could generate a 5 MHz clock!) but with occasional interruptions by the OS I presume.
I was thinking of doing some embedded systems prototyping in which some control algorithm would be tested and results quickly plotted without having to move data to some other system, but I had trouble with compilation times being really excessive or not finishing at all because of insufficient memory.
I’m not actively messing with it now. If I tried again I would probably divide the problem - let the raspberry pi do the pseudo-real-time stuff in Julia, and let it serve data over Ethernet to a PC doing plotting and analysis, also in Julia.