How do you plan represent UTF-8 in such approach?
Your posts seems to be written under assumption of fixed-sized encodings. I understand that you come from the Windows world, but Rust has made a consious desicion to use UTF-8 as the main string encoding and supporting all other kinds of endoings in the std will just lead to bloat. And if I understood your proposal it will result in needless compexity in a lot of the code.
Do we need Windows-oriented ecosystem of crates? Yes, of course. Rust provide excellent tools for developing them. But I don't think that it's reasonable to expect introduction of drastic changes to Rust core which will make Windows developers a bit happier, but will create a ton problems for others.