I didn't intend to imply all vowels can be dropped or wild-carded in English. As far as schwa, if we do refactor English, we should probably stick to existing "normal" letters rather than introduce symbols such as an explicit schwa. I agree this risks either ambiguity, or some potentially non-obvious rules to remember.

As it is, I feel sorry for non-native English learners; English's spelling is a mess. The only saving grace is that being semi-phonetic means one can often make a decent guess.