I think this game will have it's own new starters, and be like Pokemon Emerald, Ruby and Sapphire, only some pokemons that aren't originaly from that Region. Getting starters was needed to trade in every game, except Pokemon Yellow. I think you need to trade starters like Charizard, Venusaur etc. from Ruby, Sapphire, Emerald, Colosseum, XD, Fire Red or Leaf Green, or if you have them in Pokemon Box [hope it's compatible]

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Nintendo and Game Freak can't make big money if they put every pokemon in one game, because everyone will buy that game and leave others in the junk side. So, you even need to have Pokemon Ranger in order to get Manafi, and I hope you can complete the PokeDex without it, like for Jirachi and Mew. With this I want to say, I think Nintendo will never make a pokemon game in which you can get every pokemon.