Not sure how that's mutually exclusive. Magearna informs people of how to construct Pokeballs, and Apricorn balls were one of the early prototypes. It could also be convergent design, where the people of Johto discovered the properties of Apricorns independent of Magearna.
Actually, I think that would be rather clever. I don't think Complete Zygarde would really work as a version mascot for a "Pokémon Z," for the obvious reason that it looks nothing like a Z. I think all of the Zs we have going around are big red herrings no matter what the next games turn out to be. But "Mega X and "Mega Y," with Mega Xerneas and Mega Yveltal on the covers, would make a lot of sense. They would, presumably, actually match the titles in their aesthetics, and they would be cool, new, relevant cover mascots that haven't already been paraded around in the wider media for months beforehand.
Zygarde could and probably would still be involved in the plot, of course. But perhaps the plot trajectory would instead move you toward obtaining a Xerneas/Yveltal and Mega-Evolving them in order to defeat Complete Zygarde (remember that it is said to be stronger than base Xerneas/Yveltal), and then you could encounter it in it's 50% Forme in the post-game and access its other forms from then-on. So basically just like Kyurem in B2/W2.
It's still no joke even next to Rayquaza, Fairy-type Arceus can still wreck that thing anyhow lolYeah, but now the Pokémon that's said to have created at least a planet looks like a joke next to a dragon that controls the wind. It's the principle of the thing, ya' know?
I don't think that's a relatively new thing for Mythical Pokémon that aren't supposed to be known by the players. Arceus was never mentioned in-name until you had one for the required events in HGSS, last I check for an example, and aside from Mew in the Kanto games I don't remember any other Mythical being mentioned outside of the events that involve them. It's very likely that their mark can just be left as a hint to those who know about their existence, but nobody in-universe knows because they've never seen them before.
Perhaps the connection is simply incidental. Perhaps Carbink's crystals and the crystals of the Anistar Sundial are made of similar materials, and the event 3,000 years prior was what resulted in both the pink crystal for the Anistar sundial and the original Carbink mutations that lead to Diancie.
I feel like that was done to tie in with the movie, and also partially as an excuse to give us the Legendaries (obviously). While I'm not trying to vouch for the significance of the rings in relation to Hoopa (though the connection is super-obvious), Hyperspace Fury pretty much shares the same ring model as the battle animations from a legendary Mirage Spot. Of course, unless you were to get the appropriate Hoopa Unbound, you wouldn't know that without watching someone else who had it or watching the movie.
They're not really special locations more than they are just dialogue triggers (obviously with items included for some of them), and though it's nothing to do with the significance of them in the story, I'm happy with it being this way because I'd end up feeling less bad about the idea of resetting my game. At least I won't have an event-exclusive location that I can never go to again... Looking at you, Birth Island.
They called it "Pokemon Anniversary Game" so its name is closer to the naming convention for something like Yellow Version which is officially called "Pokemon Yellow Version: Special Pikachu Edition".
If it is a real leak, then I'm pretty sure Rainbow will have some new Pokemon though.
