Not sure what I think of this yet, but the VGC 2016 rules have been announced.
- All battles will be Double Battles played in Pokémon Omega Ruby and Pokémon Alpha Sapphire.
- Time limits for battles will vary by event. At major events (Regional Championships and above), battles will have a 15-minute time limit, 45-second move timer, and a 90-second Team Preview.
- Pokémon brought in via Poké Transporter will not be permitted (the blue pentagon is required).
- All discovered Pokémon will be allowed except the following Mythical Pokémon: Mew, Celebi, Jirachi, Deoxys, Phione, Manaphy, Darkrai, Shaymin, Arceus, Victini, Keldeo, Meloetta, Genesect, Diancie, and Hoopa.
- Teams may have no more than two of the following Pokémon: Mewtwo, Lugia, Ho-Oh, Kyogre, Groudon, Rayquaza, Dialga, Palkia, Giratina, Reshiram, Zekrom, Kyurem, Xerneas, Yveltal, and Zygarde.
- All items will be allowed except Soul Dew. Each Pokémon must hold a different item.
usage statistics from the "Generation Showdown" Online Competition (similar format)