So, Additional Resources seems to say Mutation Warrior is both available and not available for play.
Archetypes: all archetypes on pages 75-133 are legal for play, except forgepriest, hex channeler, musketeer, mutation warrior, packmaster, primal companion hunter, primalist, spirit summoner, and steel hound. Hex channeler, mutation warrior, and primal companion hunter are now legal for play. The free crossbow by the bolt ace's crossbow maven ability is not made of any special material and is worth 22 gp if sold.
As far as I can tell, this was re-opened as an option after they were errata'd to change the level at which you get Mutagen from 1st to 3rd - which seems like a sensible change.
Am I correct in interpreting that the post-errata version of Mutagen Warrior is now PFS Legal? The current text seems like a needlessly roundabout way of saying that it is.