anybody done this before?

[blumpkin blownuts]

pro tip except for like one page of source code, there is no reason whatsoever to use an assembly language to write an operating system

Not for the whole thing, mainly just its assembler.
That's used to break down HLL's into chunks of assembly code, used by the computer at the machine level to control/compute data.
I'd also expect it to be kinda difficult to memory-map and table addresses for bus components like I/O, DMA etc without an assebler.
Then again, maybe there's some bloated one-size-fits-most HLL library that can directly access all memory & memory-mapped devices and bypass the assembly layer completely; in the process soaking up alot of unnecessary clock cycles to run the same program. You'll notice this particularly when trying to "port" user software from one architecture to another without actually rebuilding it from the machine level, for a completely alien instruction set.

It happens all the time.

If old console games were all written assembly (and they virtually all were, up to the mid 90s) they would've looked like dogshit on SNES compared to megadrive version, or vice versa, and that hasn't really changed despite that modern video games are impractical to code in asm. So now, even new games generally look/play best on 1 of the three leading game consoles, depending on how well the HLL they used to program the game compiles and assembles on those platforms.