I thought I'd propose this as a way to spice up the endgame a little bit:

At present, if you go wandering around with a powerful PC in a high DL area, most of the monsters are still going to be so far beneath you as to be completely pointless to fight--there are a fairly large number of rats and goblins and hill giants and things--basically monsters that are completely interchangeable for a high level PC in that they die in one hit, are incapable of harming you, and give no xp.

Emperor liches, lich kings, ancient dragons, great wyrms, greater molochs/titans, unicorns, doppleganger kings, ghost kings, quickling kings/queens, ki-irins, frost giant jarls, stone oozes, balors, etc.--pretty much all of the dangerous high DL monsters---are pretty rare except for those that show up in greater vaults. In a typical game, you're probably not going to see more than one or two of the guys on this list spawning randomly. What I'd like to see is that high DL areas have significantly reduced monster generation rates of low level monsters, and that the distribution skews toward the monsters that are actually interesting to fight.