Something like Mart's mutant mod that amplified the quantities and types of encounters in the game world like in FO3, I wanna fight a flock of dragons, damnit!

Something that increased the quantities of townfolks and especially the taverns, like I wouldn't expect to see dozens of NPCs in at 9am but at midnight friday night, it should be packed.
The ability to further customize how your houses' furniture is laid out, like not just 'buy a bedroom set' but buy 'two more mannequins for the basemant pls.' type configurations.
The ability to pick where your house carls hang out, I know they're supposed to hang around their particular house but the idea of a real base of operations with a half dozen NPCs living there is cool.
Lofty and ambitious: automagic dungeon generator that'd mix up not just the encounters but the layouts of a few otherwise generic dungeons/caves.