We may consider this option if it becomes absolutely essential.
The addon would need to be completely rewritten to accommodate all the new post-MoP information (breeds, quality, level, pet names, etc.). Plus, then we'd have to maintain two systems for allowing people to update their collections. We did this before and it was problematic.
So for now, our hope is that Blizzard will continue to repair and maintain the Armory, as it offers our site (and many others) data and functionality that would be difficult to replicate via an addon alone.