Recently I’ve been thinking about what the Pokemon Go game might look like in a few years, and also what’s been holding back Niantic from releasing more Pokemon.
There are 7 generations of Pokemon, so there’s no way they’d be able to get away with piling them all together. Drop rates would be too low, the game would be messy and there would be no progression through the generations for newer players.
What they could do, is base it on level, but then if you missed a Pokemon before progressing, you’d be stuffed (unless there was a trade system, but that could be abused of not implemented correctly).
An alternative could be voluntary progression, perhaps on a trigger like level or number of Pokemon caught.
Another option might be too have a portal system in the game, to allow trainers to travel to the next generation. After traveling through a portal, your Mario color could change and different Pokemon would appear. I think that would be the most fun, because trainers could start almost anywhere and jump about to catch their favorites before completing their sets.
I heard (unauthoritive) talk that generation 2 will come out in May 2017, so it will be interesting to see how it’s implemented.