I'd love it, really love it if a Sensible Soccer (a 2d football Amiga game) homebrew game was made. The DS touch screen could be used to move the player around and kick the ball ala Big Bang Mini. With wifi to boot!
Also a Magic:The Gathering homebrew game would be lush. I know that one exists for the PSP and a card viewer homebrew application exists for the DS, but, there isn't a game for the DS. I don't know why Hasbro hasn't already made this seeing as Yu Gi Oh is such a popular title and Magic has the same basic mechanics that YGO has.
And...........................
Naked Anime Chicks Pro. Wrestling RPG. Done like Pokemon.
You start off as a lowly street pimp, trading/training whores and getting them to battle against other street pimp's wrestlers (naked stylee), gaining respect (to use more exp. wrestlers with and to go to bigger towns) and money(buying clothes,etc.) as you win. The cities would be where the tournaments are held and where the more exclusive pimping items are (fur coats, bling, porn stars).
Eventually you become king of the pimps and take on a rap career or maybe a MTV presenter job!