User blog comment:Jimeee/Hearthfire confirmed as the latest add-on. Official trailer./@comment-90.215.96.212-20120828211318/@comment-1600847-20120828212106

Actually, the idea was there before Skyrim was released. According to Todd Howard, they had a week at Bethesda where they just "went nuts" and every designer made a little something in that week. Spears, Dragon mounts, seasonal weather, more realistic water currents, crossbows, and a lot more. Some of them got put into Dawnguard, some will be in future DLCs.