X# is a HLA (High Level Assembler) for X86/X64 (ARM coming) assembly language
Might not be able to port Cosmos yet but if ARM support arrives then maybe.
I think in the LInux world .NET is Mono?
A google shows Mono seems to have better Arm support?
.NET/Mono is not a language I have used on Pi's.
Rewrite Cosmos in Mono and try compiling it?
How much rewriting is needed?
Could it be used as baremetal OS for Pi's?
That has my attention.
Oh goodie, Mono can talk to OpenGL
That means accelerated graphics for the OS?
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges