VelvetViolet
Adventurer
One of the good things Pathfinder did was reduce the number of types by making Giant a humanoid subtype and Elemental an Outsider subtype.
However, I don't think this goes far enough. Several of the types can be easily reclassified as subtypes of another type based on the same rationale as giants and elementals.
Oozes are basically amorphous Aberrations, much as elementals are amorphous outsiders, and plants* would also qualify as aberrations, since their anatomy is utterly alien compared to animal anatomy (incidentally all three have the same HD/BAB progression). Creatures with the plant subtype are generally not normal plants that could be expected to exist in the real world, but are "aberrant," such as possessing the ability to walk on their own or attack and eat other creatures. "Normal" plants that don't violate real-world anatomy and are just dangerous to be around because of poisonous spores of some such are better classified as hazards.
Monstrous Humanoid and Magical Beast are just magical/better versions of humanoid and animal, respectively (e.g. a centaur is just a human with a horse lower body). In fact, they could just be condensed into a general monstrous/magical subtype that can be applied to humanoids or animals to give them better HD/BAB/skills. Dragons are just reptilian magical beasts except with better stats because dragons are just that awesome. Vermin are just animals with no intelligence score.
Monstrous Humanoid, in particular suffers from poor distinction from the humanoid type. Many humanoids have monstrous or animalistic features, but are not monstrous humanoids. The only real difference between the two is that monstrous humanoids have better stats and are immune to effects that target only humanoids, which has questionable logic behind it (why would a centaur be immune to charm person despite having the same basic psychology as a human?). Saying that this change shouldn't be made because it would overpower shapechanging spells no longer qualifies as a defense because PF changed the way those spells work precisely to prevent such things from happening.
Even construct and undead could be combined (since they already share so many traits already) or undead made into a subtype that can be applied to many of the other types rather than changing them to undead.
However, I don't think this goes far enough. Several of the types can be easily reclassified as subtypes of another type based on the same rationale as giants and elementals.
Oozes are basically amorphous Aberrations, much as elementals are amorphous outsiders, and plants* would also qualify as aberrations, since their anatomy is utterly alien compared to animal anatomy (incidentally all three have the same HD/BAB progression). Creatures with the plant subtype are generally not normal plants that could be expected to exist in the real world, but are "aberrant," such as possessing the ability to walk on their own or attack and eat other creatures. "Normal" plants that don't violate real-world anatomy and are just dangerous to be around because of poisonous spores of some such are better classified as hazards.
Monstrous Humanoid and Magical Beast are just magical/better versions of humanoid and animal, respectively (e.g. a centaur is just a human with a horse lower body). In fact, they could just be condensed into a general monstrous/magical subtype that can be applied to humanoids or animals to give them better HD/BAB/skills. Dragons are just reptilian magical beasts except with better stats because dragons are just that awesome. Vermin are just animals with no intelligence score.
Monstrous Humanoid, in particular suffers from poor distinction from the humanoid type. Many humanoids have monstrous or animalistic features, but are not monstrous humanoids. The only real difference between the two is that monstrous humanoids have better stats and are immune to effects that target only humanoids, which has questionable logic behind it (why would a centaur be immune to charm person despite having the same basic psychology as a human?). Saying that this change shouldn't be made because it would overpower shapechanging spells no longer qualifies as a defense because PF changed the way those spells work precisely to prevent such things from happening.
Even construct and undead could be combined (since they already share so many traits already) or undead made into a subtype that can be applied to many of the other types rather than changing them to undead.