When guild housing comes along, I'm hoping that one thing they do is go back and add trophies to display in the guild hall. For example, when you kill Velah, you can then display a mounted red dragons head somewhere in the hall. One per guild.
It would also be nice if they offered banners for the guild house, that you could pick from some premade designs, or use a design of your own, so that INSIDE the guild hall, it's personalized to your guild.
Being able to also decide what kind of interior would be cool as well. That was something in EQ2 about housing that was a nice touch. You could change the look of the walls and floors. So you could have stone or wood or plaster walls.
Being able to customize the look of guild halls would be great.