For any possible future Pokemon X and Y tournament events, I'd recommend this:
Standard Singles Pokemon Battle, Each player has 6 Pokemon
Matches are only best of one, Finals matches can be best of 3 depending on how the host decides it.
No coaching, advising, or consulting between players is allowed during matches. Anyone found to be either giving or receiving advice will be disqualified and penalized in the standings. Collaboration on team building before the tournament is acceptable.
The following clauses must be enabled for all matches.
A player cannot have two of the same Pokémon on their team. For example, a player cannot have two Koffing on his or her team.
A player cannot put two or more different opposing Pokémon to sleep using attacks that induce sleep to opposing Pokémon.
A player cannot increase their Pokémon's evasion stat with a move that specifically increases evasion. Items or indirect boosts do not break this clause.
Players cannot use moves that have a chance of instantly KO opposing Pokémon. For example, Horn Drill is an illegal move to have on a Pokémon's move set.
Self-KO clause: The player automatically loses if his last Pokémon uses Selfdestruct or Explosion. Destiny Bond and Perish Song also fail when used by the last Pokémon.
OU (This is good to some degree, but now that there's a new Generation it's outdated for the meantime)
Banned Pokemon - A team cannot have any of the Pokemon found in the following tiers: Ubers. (http://www.smogon.com/bw/tiers/uber
Banned Abilities - A team cannot have a Pokemon with any of the following abilities: Sand Veil and Snow Cloak.
Banned Items - A team cannot have the Pokemon Latias or Latios with the hold item Soul Dew on their team.
Drizzle + Swift Swim - Using both a Pokemon with Drizzle and a Pokemon with Swift Swim on the same team is banned.
Since that Ubers list doesn't have any 6th Gen Pokemon yet, Xerneas and Yveltal will definitely be joining that list of Uber Pokemon.