I posted an idea for this a while ago, but I'll post it again here:
Make the GTT (Guild Tower Tournament) where there are 3 separate towers in one large, enclosed area. Then allow the top 5 or so guilds of the season to participate. The team that holds a tower for the longest amount of time in a 24-hour period gets a prize.
Something along those lines anyway. Number of guilds, towers, or time-holding may vary. I think it would be interesting to watch or participate in. I'm not sure how easily this would be implemented though, or if it would even work very well. Feel free to critique it or add anything.