Here is a Famitsu translation for details about the second season for Pokemon Best Wishes:
If Meloetta becomes a character that travels with Ash and friends, then perhaps it could end up becoming the face of Black/White 2, and thus have a leg up over Zoroark/Victini for the Pokemon newcomer spot. Meloetta has the gimmick of transforming between its Aria and Pirouette forms, and Sakurai has put in a character in Melee and Brawl a character with a transformation gimmick.
According to the summary on Famitsu, the gang along with the Shin'ō League Champion Shirona will head to eastern part of the Isshu region, which has many non-Isshu Pokémon populating it. They also encounter Hikari, one of Satoshi's previous traveling companion. Meloetta will later become Satoshi's friend and journey with them.
Cattleya, one of the members of Four Heavenly Kings of the Isshu region, will enter the World Tournament Junior Cup along with Shirona. The winner of the cup can battle Isshu League Champion Adeku.
Along with that, Satoshi will also have a new rival, and Sakaki will lead Rocket-dan in their 'biggest plot in history'.
If Meloetta becomes a character that travels with Ash and friends, then perhaps it could end up becoming the face of Black/White 2, and thus have a leg up over Zoroark/Victini for the Pokemon newcomer spot. Meloetta has the gimmick of transforming between its Aria and Pirouette forms, and Sakurai has put in a character in Melee and Brawl a character with a transformation gimmick.