I've always wanted there to be HP+ and HP- natures, maybe HP will have IVs?
HP IVs already exist. Although if they're changing things up, I wouldn't be against new natures. There's probably some horrible problem with HP natures I'm not realizing right now, but right now all I can think of is making the odds a little worse for getting the exact nature you want.
It'd be a useless nature on shedinja.
It'd give Blissey almost 800 HP.
Those are the only things I see wrong, if that, not that there's anything wrong with a more HP bulky pokemon.
Any +defense or +sp. defence nature is also useless on shedinja, so I think that part is a non issue.
But the defense ones still alter a value, whether or not it has a use is something else altogether
"Why do I check for updates when I know there's nothing there?"
1) Flag gen 5 Pokemon so their hidden power is calculated with the old formula. New Pokemon are calculated with a new formula that includes Fairy type.
You know, there IS a precedent for this. In Gen V, abilities are calculated in a different way than they were in Gens III and IV. Transferred Pokemon actually are flagged a certain way that lets the game know it has to calculate their ability the old way. This prevents Pokemon with two abilities in Gen IV from possibly switching to the other ability line if they evolve in Gen V.