@velartrill
I guess having X written in X helps with development as you only need to know one language very well to develop it (less cognitive load?). And any advancement in your language reinforces your ability to further develop it. Rust was created to address problems with C++. Also first compiler was created in ML for a reason.

For what I know portability issues are mostly to do with LLVM missing support... if you have any links, I would like to learn more.