As for the six Pokemon limit, I'm personally against altering the laws of a universe merely for the sake of convenience, but again, a topic for another thread. Mainly, I just don't quite see why it would make sense from a trainer's standpoint. Most trainers don't start forming coherent teams that covers its type weaknesses and has specific roles for each member (wall, tank, sweeper, whatever) until quite a ways into their journey, simply because the Pokemon you may need aren't all accessible in the "early" parts of the region. So you either hold off on catching a water type until you find a Lapras you so badly want, thus eliminating your potential advantage over the fire gym you have to face next week and also giving you a disadvantage over other trainers with full parties, or you catch a Goldeen who you only want as a temporary member. But if you're limited to six, how are you ever going to get that Lapras?