We have many words that are spelled the same, but sound different based on context, like "sow". That isn't a problem. They don't have to be differently encoded. Besides, are you now planning on adding accents and dialect pronunciations, too?
I'm not talking about homonyms (but I wasn't clear enough about that, sorry). I'm talking about the exact alphabets describing pronunciations. Honestly I can't really differentiate [hɑt] and [hat] sounds, but their IPA renditions are clearly different and have to be differently encoded.
So you have two different pronunciations [hat] and [hat]. Which one is which? Do you really expect to say "[hat] as in General American hot" and "[hat] as in Received Pronunciation hat" every time? Isn't the IPA supposed to be an unambiguous transcription (so to say)?
It’s a fake problem if you just want to write the word “sow” or “hat”, sure, but if you want to write the IPA pronunciation of a word you need the IPA characters in your charset.
Wikipedia has those IPA pronunciations and they’re useful. How else would you do that without including those characters in Unicode? Would you rather have them as images?
