In theory, I wouldn't mind if another iteration came out. In theory. I also thought Pokemon Pinball R/S was going to be a lot more inspired than the original Pokemon Pinball. But out of the two, I get a lot more joy out of playing the original.
For Pokemon Snap 2 to work, it would have to build upon and expand from the original idea. If the game just ends up being the same length with 60 Pokemon, it's just wasting everyone's money, Nintendo gimmicks aside.
Don't get me wrong, I really liked the original, and if they did it right, I might even buy a Pokemon Snap 2. But by allowing you to take photos in games like Rumble and Ranch, they really can't be chintzy or stingy about the amount of Pokemon they allow in the game. I get it with the Pokepark style games, since they're all built around a planned story of sorts, but if I'm gonna take pictures of Pokemon, I want ALL of them. Everyone wins that way. People who only remember the first handful of generations don't feel left out, and people who were weaned on the newest Pokemon don't feel isolated, either.
The gameplay can't be a carbon copy, either. Innovate, and come out with new ideas and new ways to play. Maybe create a sense of randomness, so that each time you play through, the Pokemon aren't always at the exact same location doing the exact same thing or triggering the exact same events. A time of day system would be pretty sweet, too. I don't mind the on rails gameplay, but perhaps you can select a few different tracks or routes per environment. Didn't see any Pokemon in the straight line path in the desert? Maybe they're all over by the oasis because they're all reasonably hot and thirsty. Take the tram that swings around the oasis.
Overall, if it's going to be on the Wii U, there's really no excuse for limitations.