I, too, was very disappointed in the lack of even the shallowest of storylines for the single-player of Bomberman DS, which ultimately influenced my decision to not buy the game. Yes, I am one of those freaks that likes Bomberman single-player. Perhaps part of it is that I rarely have anyone to play multiplayer against...and in general I'm a loner.
Anyway.
1. I wish they'd bring back Lilith, Rukifellth, and the Elemental Knights. They had so much potential in the Second Attack storyline. Or even Princess Millian and Nitros. There's so many one-shot characters that could be developed (though I'm aware this also runs the risk of being butchered and re-hashed). Though I love Jetters to death, I think there's also a lot to be done with the existing "original" Bomberman material.
2. I want to see Bomberman Kart Racing for a Nintendo console. If they brought that back, I'd so buy it.