They do not coexist until the first time the new one is used. My point is still valid.
Either you’re talking about a completely new pronunciation being invented (and are the only one talking about this), or you’re saying that the dialectical variant with the shorter history is the incorrect one. In which case, ‘height’ loses out to ‘heighth’.
(Plus the condescending assumption that pronouncing a word in a different way indicates an inability to spell it.)