In reply to A Latin Abugida:
If you're trying to differentiate sounds of the same phoneme (like /pʰ/ and /p/ in English), you might need more symbols:
Seriously, even IPA, with its plethora of characters, cannot claim to have 1 character for each sound (/pʰ/ is a counterexample). I don't think Devanagari has a chance here.