I think that this is the sequel to XY and is still a part of the sixth Gen. Think about it for a minute. With every new Gen, the first stage of the Starter Pokemon is always revealed, right? So why were we not shown any new Starters? And having something to disrupt the sun and moon CAN cause ecological disturbances which could make Zygarde angry and come out of hiding and have a part of the main story like how Groudon and Kyogre did in Emerald. It may not be the main Legendary but it's lore could be explained more. I think this is a direct sequel. And I bet Pokemon we already know and exist can be put in the Pokebank and be transferred that way like how XY and ORAS can exchange Pokemon this way with some limitations. Trading and Battling may also be limited to exclude new Pokemon and Mega Evolutions. The mentioning of Poke Bank transferring never confirmed that Sun and Moon won't have direct interaction yo XY and ORAS.