The featural writing system (first used in hangul) is a writing system in which the glyphs themselves contain phonetic information in the characters. It is widely agreed by linguists and conlangers that featural writing systems are the epitome of writing, but unfortunatly the first was created in 1500 AD, as opposed to the ancient quality of logographs. No one can deny the appeal of having an old age culture having this system, but could they?

When is the earliest I can hope for a culture to create a featural writing system?