Fel Pups might not get crazy expensive with how easy Nethershard farming is, but they're a bit different. Iron Starlettes are still obtainable and given by a questline that pops up automatically for most characters. Fel pups are planned to only be available during pre-patch.
Nether shards likely won't have a use in Legion. I'd just grab the appearance kits and the BoA glaive now, and then fill one line in you guild bank with the pets for later purposes.