|Yes, get in the fucking bag, Nebby!
(Spoilers for Pokemon Sun ahead, serious end of plot spoilers)
What if Lillie became a trainer down the line? What if she moved to Kanto with her convalescent (and quite probably necessarily amnesiac) mother?
Maybe that would make a cool roleplay run idea: to replay the series from Kanto to Kalos as Lillie on her own Pokemon journey. You'd have to use the Gen 1 remakes since the originals don't feature a female player character but upgrading to colour sprites can hardly be termed a hardship, unless you're my co-worker Dan who swears Pokemon Yellow is the best in the series and still totally holds up.
Still, whether as Lillie or a character of my own creation, the idea of playing the games in order appeals to me. I played the original game when it came out but after that I jumped all around the series after intervals of years. In fact, I've never played the Gen 2 and 5 games. I also have a naughty copy of the fan game Pokemon Uranium on my laptop just waiting for me to give it a try (another recommendation from Dan the Pokemaniac).
Just spitballing ideas here, really. I mean, aside from Gen 5 I do have all the games lying around and the only ones I've ever completed were Red and X. Might be interesting to create a character, Ash style, who would travel the different regions on a quest to become the best there ever was.
Maybe even have a rule (again, just an idea and rather based on the anime's approach) to never have the same Pokemon on your team in two different regions. I don't see this trainer having their own version of Pikachu, if only for the fact that other the internet informs me the only Pokemon to appear in every game are Zubat, Golduck, Magnemite and their evolutions. Pikachu, to my surprise, actually skips Gen 5.
If nothing else, completing X and getting as far as I have in Sun has made me appreciate that these games have pretty decent plots and I'd rather like to explore the evolution of the series the way more dedicated fans than me have: in order, from the start, with progressively cuter starters and progressively more insane final forms.