I don't know if local dialects are the reason it wouldn't work. But major dialects—as in UK English, US English, India English, etc—would probably be the sticking point. Small differences, like a u in some words or using "jumper" or "sweater" are just curiosities, but if each major dialect started spelling completely differently, it could quickly make a mess. Well, an even bigger mess than we already have.
Yeah, I don't expect it to ever happen. This is more just a thought experiment.