That was really interesting, you put a lot of efforts into that !

I use mksh myself, mostly because it is light on resources, and less subject to bugs than bash or zsh (which have features I don't use anyway).
I find it interesting that you ended up using tcsh, because the syntax is REALLY different from standard POSIX shell language. It basically means learning a new shell scripting language, even though you only use it interactively and for a few use cases (looping through files, etc…). How do you feel about that ?