What I think would be great is if they actually break out of their tradition some day, and give us starter selections that are not fire, water, and grass. I know that these are our basic ones, but they must not limit themselves to these typings just because of that--seems like a reason for them to not try something new, and just stick with their same, old formula. Dragon, ghost, and fairy would be decent combination, if you ask me, considering how popular they are among fans. Another is steel, ground, and ice; they're all super-effective against each other, I believe, which would make a perfect balance.
These two are just examples--if we think hard enough, we'd be able to come up with a variety of combos. It's all up to them, though, if they actually do wish to do this or not. Personally, I'd love to see it happen!