What do you think the next step with Garrisons will be?
1) guild districts? (in main cities)
So a new part in the main cities (Orgrimmar - Stromwind) what will still be instanced but your guild members houses will show up when you get in the district alongside your own house. Maybe the guild needs to work together to place statues and street lights outside on the roads.
2) guild zepplins/airships?
Moving fortress for guilds to gather in and class rooms on board where classes inside the guild need to work together to design there room.
Maybe even add guild PvP and exploration quests into the mix
3) Another garrison but with different races in mind?
Same concept but the art will focus on another race.
4) Other idea:
5) Garrisons will not be a feature past WoD