Many people have been saying that PLZ-A will take place during the mid 1800's because that's the time period when the renovation of Paris happened. Don't get me wrong it's definitely inspired by the renovation, but it doesn't make sense for it to be reconstructed for people and Pokemon to coexist, then become incredibly human centric by the time of X&Y for no reason. The sketched out plans and holograms in the trailer also make it seem like something that's planned to happen rather than something that has already happened in the past, the music also sounds very modern.
All this leads me to believe that PLZ-A will be a B2W2 like sequel with returning characters such as Trevor working for Professor Sycamore, Emma as Essentia, etc.