So, I've had this question for a couple of other things before, but I never thought to put it up here, and I'm looking at the Shifter now and it made me think of it again.
Shifter's Claws. Start at a d4, eventually go up. Improved Natural Attack. Raises a natural attack by a die of damage.
So. Shifter's Claws at 1st level, I now have d4 claws. If I take Imp. Nat. Attack at level 4 (or the closest time I can get it), do they become d6, and then go to d8 at level 7? Or would they just stay at d6 and I'd 'skip' that upgrade?
*Edited - Title clarification
At 4th level you have d4 + INA = d6. At 7th level you have d6 + INA = d8. Etc. It's not that INA bumps you up and then the class bumps you up again---INA has no idea what the class is doing, it just bumps up whatever is provided. If the class took you directly to d8 at 7th for some reason, you'd get d8 + INA = 2d6.
Hope that made sense.
So in other words, it is a feasible feat to take. Gotcha. I tested it out with my HeroLab and the Barbarian's animal totem powers, too (I don't have UW for HeroLab yet) and it worked, but I wasn't sure. Thanks