I'd also love a museum update, but I want enough done with them that it'd probably be a full game pack. At minimum, an active career working at the museum, field trips for HSY, and a return of the TS3 time machine (for museum workers to do research in the past or grab artifacts, for high school students on field trips to sneak into, or for engineer or scientist characters to invent).
On a more "updatey" sort of thing, better matching wood swatches, especially on stairs, pillars, and foundations, and fix the kitchen islands that have the cupboards on the wrong side.