I know smithing/enchanting services exist as mods for Skyrim, but the main shop that I always wanted in Skyrim was a bookstore. I'm a massive sucker for lore and normally have my characters collect books like madmen, and I really missed browsing bookstores in Morrowind, where books were quite expensive and heavy. It might be a small thing, but I also would like to see stores/places that make towns feel like towns, like a baker's or butcher's.
Mods help this sort of thing, but mods exist to show Bethesda what they should put in the next game.