I would LOVE a multi-location vacation pack. Though I know if we got a full blown multi location pack it would just be for two locations at most, I'd love more. Even if the worlds were small say a dozen or less lots a piece. There would be a complete hotel or resort system as well, for all of the locations.
The locations:
Las Vegas Style with hotels and casinos - 8-12 lots, four casinos in total based on approximations or with licensing actual resemblance of existing casinos. Each casino would have two lots, one for the hotel/casino and one or two for an entertainment/attraction/restaurant of some type. Total lots 8-12
Winter resort vacation - although this sounds like we'll be getting it in a GP/EP, a romantic ski resort get away with ski lifts and downhill skiing, a hotel resort. Maybe two resorts, one upscale and one more of a "getaway" location, and 4-6 or so activity based lots. They could introduce a new type of lot that is very long but very narrow, longer than we've ever had, for the skiing. People that did not have seasons would have access to the snow IN THIS WORLD ONLY. That way it wouldn't require you to have seasons. Total lots 6-8
Egypt or something approximating: I just love the pyramids so something like that would be neat. Very much like with Sims 3 World adventures, this would be more of an adventure location than the others. There'd be a hotel, and three pyramids each with their own adventures, and also a centralized market lot or 2. Total lots 5-6
Mediterranean beach side resort: NOT on a island, main focus is just to get away and enjoy the coastal life. Explore Grecian ruins, lots of Grecian architecture, they could have one large resort lot with a another lot or two with resort activities, and then another 3-2 lots to explore ruins. Total lots: 5-6
Total worlds 4. Total lots 24-32
I thought about an African safari location as well, but as that would also HAVE to incorporate animals I don't see that happening within a pack that has other things going on. It could be an interesting GP by itself though.