Can a human take the Racial Heritage feat to gain the kitsune subtype? If so, do they also add the shapechanger subtype? Finally, would they be able to qualify and use the Fox Shape feat (prerequisites: Cha 13, base attack bonus +3, kitsune)?
I too would like to know.
Definitely yes for the first question and no for the second one.
There is no question that a human with Racial Heritage (Kitsune) would qualify for the Fox Shape feat. Until I actually got a look at the feat, I would have said that you wouldn't be able to use it -- but it appears that the feat makes no reference to the Change Shape racial ability that a human doesn't have, so on that basis it appears that it should work. The one part that could pose a problem is the bit about your bite damage being reduced to 1d3 -- how do you reduce non-existent damage? In any case, the correct bite damage for a fox is 1d3 + Str mod, so that damage die would be correct for the Beast Shape effect described for this feat.
So, if I go by Blackbloodtroll's logic, while the character may be treated as a kitsune for the purposes of traits, feats, how magic items affect them, and so on, they do not actually gain the kitsune or shapechanger subtypes.
I can understand and agree with that. The wording of Racial Heritage only says they are treated as such, not that they actually gain the subtypes.
For the Fox Shape feat, however, that is a little dicey. We can all agree a character qualifies for it. However, the shape changing nature of the ability is clearly supposed to be linked to the Kitsune's change shape racial ability. Unfortunately for GMs everywhere, the feat makes no mention of requiring that ability and only touches on reducing the bite attack of the kitsune to 1d3 (because the kitsune has a natural bite attack).
I believe I would go with David Knott 242 in you can use the feat to change shape into a fox.