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Now that the dust has settled about Paradox Pokemon being from alternate timelines (so they're a cross between UBs and regional variants), does anyone want to see actual past and future Pokemon? No robots, no forced 570/590 BST, no minor tweaks... They would follow Darwinian evolution. Maybe alternate evolutions like Kleavor are the closest examples we have, but they lack lore.
The best setting for this kind of concept would be a Legends game, but Game Freak played it safe with Hisui by sticking to regional variants. Perhaps the game was not set far enough into the past. Luckily, if get a Legends Celebi game, we could get a lot more flexibility with time travel. If Game Freak are interested in that at all, they should really do it to wrap up this generation (and maybe make up for the Paradox mess).