This is basically impossible for English, since for many vowels, the various dialects map the diaphonemes of English into mutually incompatible sets of phonemes

This is basically impossible for English, since for many vowels, the various dialects map the diaphonemes of English into mutually incompatible sets of phonemes: https://en.wikipedia.org/wiki/International_Phonetic_Alphabet_chart_for_English_dialects#Chart https://en.wikipedia.org/wiki/International_Phonetic_Alphabe... (and even that chart is underestimating the differences - tour and moor definitely have different phonemes in en-AU, even though they are allegedly from the same diaphoneme. If you had a conservative spelling system, where each diaphoneme was mapped to a single letter, speakers of dialects with many merges (e.g. American English) would struggle to spell correctly, since they would be unable to distinguish several letters apart. If you had a simplified system, then most speakers would get confused by merges that existed in the spelling system but not in their own dialects; and speakers of more conservative dialects wouldn't be able to write sounds that are to them different.