As a general rule, the staff here at Pokecharms try to avoid passing comment on other fan sites. We do not link to other sites except for our affiliates. However, in this case, there is proof from elsewhere that Serebii is trying to cover his arse.
I can't find a link right now, but several months ago Japanese fans found a list of new trademarked Pokemon names in Japan. By their legal definition, trademarks must be published, although searching them is rather tedious. Every time they want to release new licensed products, Nintendo/GameFreak/The Pokemon Company trademark the Pokemon names which are going to be used. Therefore, before each new game, people look out for the trademark lists and claim them as a "leak" of new Pokemon names - although given their standing in law, they must be taken much more seriously than other "leaks".
Here's the list, copied from
a post on Bulba forum since I can't find the source right now.
ディアンシー, Diansii
ハリボーグ, Haribougu = Quilladin
ゲコガシラ, Gekogashira = Frogadier
ボルケニオン, Borukenion
デデンネ, Dedenne
ホルビー, Horubii = Bunnelby
ニャオニクス, Nyaonikusu = Meowstic
ブリガロン, Burigaron = Chesnaught
トリミアン, Torimian = Furfrou
テールナー, Teerunaa = Braixen
ジガルデ, Jigarude = Zygarde
マフォクシー, Mafokushi = Delphox
フーパ, Fuupa
ゲッコウガ, Gekkouga = Greninja
So we have here the middle and end stage of each starter, along with the "cute" Pokemon Bunnelby, Dedenne, and Meowstic, and the yet-to-be-revealed at the time Legendary Pokemon Zygarde. Merchandising in Japan typically features the starters in all three evolutions, the Legendaries, "cute" Pokemon, and Pikachu.
Legendaries have almost identical names in all regions. This would give us three Legendaries that are yet to be revealed. Diansii = Diancie, Borukenion = Volcanion, and Fuupa = Hoopa.