I have had this idea for a loooooooooong time. I dont know if it's very good but it would definitely be a Cool add on to the game.
So when I was younger I would buy pokemon cards and one time I got a Ludicollo EX (I know thats spelled wrong) Basically the Ludicollo was Fire type instead of water. I thought holy cheesepuffs this is amazing. I always wanted Nintendo to do that. In game pokemon can have a different type, Yes this would be as rare if not more rare than a shiny pokemon. I would always love to have a Pikachu that was Ghost type or even Psychic type. I know this sounds weird but It would revolutionize competitive battling and change it completely change it.
On another note I think a pokemon game that had all five regions in one game would be great too, just my opinions on all this pokemon stuffs. xD