Not exactly the same, since WoW was supported by a subscription but it's not too hard to imagine them planning to support Destiny with continued expansions for several years.
But if it's not a MMO then how come it shares so much with one? It's online only, it splits enemies/areas so they're level-based, it's laden with kill/collect missions, and grinding for gear, it even has raids, even events I think. I think it's insanely naive to not think of it as a MMO. But then you and I have long had different ideas about what is and isn't a MMO.