Oh god I don't even want to think about Gen 7, we already have more than 600 of these little buggers. But yeah-- I'd really love the day/night music as someone said, and maybe megas for the legendary birds.
In my old yellow version-- mind you, this was when your Pokeballs could still miss, especially when your target was at full health/legendary. Caught Zapdos with one Pokeball, at full HP.