Wouldn't that be cool if whole new sections were added onto vanilla dungeons? I even remember a few years ago, someone was going to add a new section to Bleak Falls Barrow, where you could enter and exit, but the creatures and contents would stay only in the new section. Nothing ever came of it, though. I think this would be a glorious addition to the game...and increase playing time. Modders could pick and choose whatever dungeon they want to expand, and go at it! Just remember to keep the creatures and contents only in the new parts...would not want cross-contamination, which could somehow screw up the vanilla part of the dungeon.