Garrisons didn't work like housing does in most other games I've played though. In Garrisons you have a few preset locations where you place preset created buildings. The only thing you could change was which plot they were placed in. That is not the same as free placing of objects in an open map like other games offer. Not even close. You couldn't even move furniture around which is like one of the most basic things games with housing offer.
Other games offer a toned down world builder/designer with certain limitations. Garrisons was a glorified character barber for buildings and that tech isn't really based on a world builder/designer like other games do. If Blizzard is to offer a housing system based on their world builder/designer then the original tools made for the engine need to be simplified substantially, which as Biomega mentions, might not be as easy as you think with old patched engines such a WoW's.