Unless I'm mistaken, this should be the very first reveal of Giratina in Gen IV, during that time Platinum wasn't announced yet.
February 2008 Giratina anime art
https://www.pokebeach.com/2008/02/c...ratina-origin-form-and-pokemon-battonage-info
May 2008 Giratina Sugimori art leaked(?)
https://www.pokebeach.com/2008/05/larger-pokemon-platinum-corocoro-page
If so, you win. (:
So, if we are following the Giratina route, we should be receiving a Cell and Core Zygarde, 10% and 100% Sugimori art around February.
Perhaps we should keep an eye to the next two Corocoro issues.
Jagold's idea (?) on the Kalos extension is rather interesting. It works, they can simply create a fourth Kalos dex with roughly 150 Pokemon, similar to the other three Kalos dexes. If we are to follow Jagold's speculation, I believe we'll be seeing the likes of Fairy-types that aren't included in XY, they are the Cottonee, the Togepi and the Cleffa line, which are the only Fairies that are left out in XY's regional dex.
Seeing how XY included all the XY introduced Mega Evolution forms. I believe we can also assume that the Numel, Snorunt, Beldum line will be included in this 4th Kalos Dex. It isn't that surprising if we receive more new Pokemon species at this stage then, it can be 70 more or perhaps 28 more to balance the percentage of old and new Pokemon in the 4th Kalos Dex. Incidentally 28 also forms a perfect 100 along the XY introduced 72 Pokemon in Gen VI. (:
Or they can simply add 89 Pokemon
in each current existing Kalos Pokedex. It's the laziest plan, but at least we have a game that has all 721 Pokemon to celebrate the 20 Anni.