User blog comment:Mckrongs/Monster Hunter 4 for the Nintendo 3DS/@comment-3315689-20130919150835/@comment-4815503-20130919160123

It could be that since Goa Magara is something you fight throughout the storyline, and Shagaru is the final Village boss, they wanted to keep Goa's true identity as an Elder Dragon secret to players, thus creating the necessary ??? classification to do so. If this is true, we might see Goa reclassed in the next game it shows up in. Then again, maybe not.

All in all, I don't think classification in the context of Monster Hunter is supposed to be anything too scientific... I mean, the Wyverian man in MHFU admitted as much when he said anything that didn't fit into other categories, like Kirin, was stuck in with the Elder Dragons.