sudo apt-get install fsharp
[...]
Need to get 22.2 MB of archives.
After this operation, 66.0 MB of additional disk space will be used.
Personally, I wouldn't call that heavy.
Remember that the 10MB figure for CoreCLR you give is just for the runtime alone, it doesn't include any class libraries. The Mono runtime is in the same ballpark.
Last I checked, Micro is too small and lacks crucial things you want for everyday development, and that is for a normal developer, not a language runtime-designer.
It was targeted mostly towards very low-specced hardware, closer to a Arduino than a Pi.
I'm guessing things like F# relies on too much things which are not included here.
Micro's interpreted, and is missing a lot of the bits and pieces of .NET that make it a real nice platform to work with. So you end up with something slow, and a fairly limited standard library.
Mono is too heavy and have millions other dependencies I dont want to grab.
Running a modern & practical functional language on RB Pi will be extremely joyful for me.