>>55492152LEGENDS is an artifact title now, it doesn't relate to anything regarding the setting's time period anymore. This is what usually happens when a vidya series goes on for a very long time or a spin-off gets too popular, the titles stop making sense.
Now about Z-A, it's apparent that we're seeing some kind of cyberization project going on with the virtual space imagery in the trailer and whatnot. Doesn't necessarily mean we'll be seeing a far future version of Kalos with previous characters appearing as aged version alongside their descendants. It will probably be just a more technologically inclined revision of Lumiose City, pretty much modern day stuff outside of the usual utopic pokemon world technology we're already used to seeing.
TL;DR: "Legends" doesn't necessarily mean "anything" as a title anymore, it's just the label we'll be seeing used to differentiate the mainline open-world action-oriented games from now on, since P:LA and Z-A are considered mainline. Z-A is going to be set in the present day, don't be autistic about it.
