Board Thread:General Discussion/@comment-5398529-20131025073315/@comment-5398529-20131031205920

The proof that further supports event legendaries is the three(four, but that leads to the same building, suggestively) locked doors that lead to other powerplants in the Lumiose Badlands. Each locked powerplant has a theme to it, being fire, gas, and rock. The Lumiose Gallery even has information about the three locked powerplants.

Looking at the rumored event legendaries' types: Fire/Water, Ghost/Psychic, and Rock/Fairy, I'd say this theory is good as confirmed.