I go for being able to buy your own house/castle. Maybe a choice between a house or a castle. That would be cool. Also I think you need a merchant that sells furniture so you could decorate it just the way you want it. Items you might want: cabinets, bookcases, chests, things to store your stuff in, weapon and armor racks for these items, beds, tables, chairs (sitable), candles, lamps, plates, mugs, plants, pictures, anything that you might want in you personal house.
Things like that would make the game more personal and really add to the role playing aspect.
Guilds sound good too. To join a guild maybe you could do certains quests to prove you are worthy to be in the guild as sort of an initition. Guilds should also sell items to the members at a discount rate. This should also include some very good items that can not be purchased anywhere else or by anyone outside the guild.