The whole idea is hopelessly tied to ascii notions of alphabet, where two functions (storage a retrieval with keys, and searching for matching keys with the UI)

The whole idea is hopelessly tied to ascii notions of alphabet, where two functions (storage a retrieval with keys, and searching for matching keys with the UI) have been conflated. What is 'case insensitive, case preserving' in Unicode for Korean or Chinese or Arabic? It doesn't remotely make sense to make some keys illegal in the file system layer for reasons of disambiguation.