Personally, something like that shouldn't be something for the special people who manage to buy a house when they're as limited as they are, not to mention this would just get around the item spaces we've been allotted by the game on its own. 140 item slots on you, and then 175 per retainer, with each person getting 2 (More if purchased)

Many people who don't share a house would get more storage that other players wouldn't get.