Is it about how we define bitcoin or who will define it?
I think neither is correct. The ultimate fate of anything like Bitcoin depends on how we use it and not how we tag it or call it. If we use Bitcoin as a vehicle for speculation, then it will be an asset, a speculative asset I mean, since this is the very definition of an asset, On the other hand, if we start using it as a means of exchange, then it will function as money and it will be money. In the worst case scenario, when no one uses Bitcoin for anything, it will be neither asset nor money. It will be nothing then.