Quoted By:
No multiple versions, just semi-randomized rosters of wild Pokémon decided at the start of the game. You should be able to get them all, just not the same way on every playthrough. You're a Pokémon Trainer on your way to get all medals and be able to participate in the League. Once you receive your first starter, there's a bunch of career paths you can actually take:
You can follow the Trainer path and go on adventures, catch and train monsters, win medals and defeat the League. This is pretty much the same as the stock game.
You can join in/opt out of gyms. Being a gym member, you start as a grunt and go up the ladder by defeating members from opposing gyms. Higher level gym members have access to gym-specific rental Pokémon, held items, events and quests. You should still be able to compete in the League, maybe being part of a gym means you win the title for your gym rather than just on you. Of course, you can't join two gyms at the same time, and if you resign from a gym and come back, you must start again from the bottom.
You could join the criminal organization on duty and try to make as much money as possible selling, stealing and trading Pokémon, organize illegal Pokémon cockfights with gambling, maybe even become head of the mafia if you do well enough.
Or you could follow the science path, and focus on completing the Pokédex and studying/raising the Pokémon rather than training them for fighting. Completely different game, kinda like extended Pokémon-Amie, with experience levels that reveal more about the Pokémon you're raising. Maybe you have to go around the world not only searching for Pokémon but also gathering stuff needed to keep your monsters healthy out of their natural habitat?
Of course, you're not expected to see every path on every playthrough, as some paths might be irreconcilable and exclusive from one another, but I guess that's a good reason to finally include more than one fucking save slot?
None of this will happen ever.