I don't really think it's fully possible to actually catch them all. At least in a reasonable amount of time. The only way I can think of is if you literally had every single game of pokemon (as well as the systems required) and just transfered from each generation to the next up until black/white then use the poke bank for x and y. That's just so excessive and unnecessary though. I really wish they would just include all of the previous pokemon in each generation to save the trouble of having to go through each previous game just to actually "catch em' all." Even if it meant holding off on another game for an extra year I just feel like if they incorporated everything there wouldn't even be a need to hack or cheat because it would all be there, accessible to the player.