At D.I.C.E. 2012, Bethesda Game Studios' Todd Howard just showed an amazing highlight reel of mods the studio built into The Elder Scrolls V: Skyrim during a week-long "game jam" after the game's release. Features like mounted combat, a lycanthropy skill tree, and one enormous mudcrab, the width of the horizon, were all shown. And that was the tip of the iceberg.
Howard made no promises that anything seen in the demo reel would ever make it into the game, whether as a title update or downloadable content down the line. But it did showcase the depth of what the Bethesda team built and a creative instinct within the team that matches the mod community's enthusiasm, stoked recently by the release of the official Creation Kit.