I think a good example would be someone who was once an archer going through the phases with changes to bows and projectiles should be given the option to respec their heirlooms because the class they originally wanted to play completely changed.
I think a guy who wants to play archer will stick to it no matter what, wouldnt he? Anyways, if you want reheirloom your masterwork items, you are quite high generation already, so with them XP bonuses, go grind 31 and then heirloom, rinse repeat
Ofcourse it sucks when you get unintentionally nerfed weapon, but hey, i guess its easier to let it go than to let some ppl respec their items again. And, as some other guys said in other topics: heirloomed items are not an I-WIN button.
(having just balanced german sword myself for now, should get masterwork soon, and even tho they made it slower, i dont mind, it still pwns
))