In theory something like Micropython could be replicated for Julia, (while it would be even more work for e.g. that MCU; I wasn’t even sure MicroPython supported any non-ARM ones). ARM (or x86) MCU would be the best bet.
Since you can call Python with PyCall.jl, or should I say, call Julia from Pyhon using PyJulia package (that’s based on PyCall.jl), it might be helpful to look into if PyJulia would work with MicroPython. It likely doesn’t because MicroPython is baremetal non-standard variant. Julia however requires an OS (currently at least) and a filesystem. I’m not sure you have any filesystem [access] with MicroPython. MicroPython also has changed garbage collection from regular Python. That it supports real-time use is interesting (and I recall based on fixed amount of memory and knowing the exact hardware/size). Getting the same GC guarantees with Julia should be possible, but I wouldn’t rely on it happening just by change.
Julia would not work directly on ESP8266 given that it uses “L106 32-bit RISC microprocessor core based on the Tensilica Xtensa”; and neither for any 16-bit despite it working on an LLVM:
E.g. even with 8/16-bit AVR having LLVM support (and working with Rust language, or getting there), that CPU, or any non-32-bit (or 64-bit), such as MSP430, will not work with Julia (see my thread in it; ans answers on how difficult and unlikely adding 26-bit support is; long term I see 8- and 16-bit CPUs as dead anyway, and would concentrate on ARM).
Only possibly workaround might be Julia2C (see other microcontroller thread where I wrote about that).