I hadn't seen that PF resource before - thanks, but it doesn't seem to account for the "broken" monstrous abilities (gaze attacks etc).
Always good to see Oslecamo's work - definitely more along the lines of what I was thinking. As an alternative to his work though, I was thinking more of reworking specific existing monstrous abilities (i.e. so that PCs start play with all their abilities, rather than progressing through monstrous classes). There might be a happy medium allowing some progression e.g. a medusa's gaze starts off dealing only 1d4 Dex damage, with an additional 1d4 per six levels or somesuch. A bodak's could deal Con damage instead, an energy-draining undead might instead deal +1d6 negative energy damage instead of inflicting negative levels, and so forth.