It would be cool if there was a world where all of the gods had been mortal at one point, and anyone alive today had a chance to become one. You just had to become powerful enough to force yourself into the pantheon. BECMI D&D certainly allowed a way for this to happen, but precious few games since have done it.
Of course, some of the existing gods would likely make a point of stomping out any potential competitors, but even they can fail. If their champion gets stomped by an ascending hero, it just might be his destiny to become a god, no matter who opposes him.
This would give long-term campaigns a great goal and even better, provide a perfect finale to a campaign, with the final game night being one or more players achieving godhood.