The only setting I'd like to see more then spell Jammer would be a 4e Mystara setting.
I'd like to see Spelljammer make a return. I have the original box set in storage, but I never had a chance to play in 2e. The wife of the DM in my gaming group that is willing to run it is violently opposed to it being played in her house (other stuff is okay), so he never had a chance to run anything in 3.x.
Before posting, ask yourself WWWS: What Would Wrecan Say?
I hope its covered on D&D Insider, means we'll get it sooner than waiting for them to release a book!
Spelljammer is a perfect "Points of Light" setting - the Points of Light are the crystal spears and the darkness between them is "the Flow"! Don't just release Spelljammer, make it the default setting!
Allergic to tinkergnomes and giant spacehampsters perhaps?
I can think of few other reasons.. or liking to play spellslingers, and then ending up in the helm.. (bad mage, bad! Go sit in the corner, while we adventure!) lol