Seeing as guild ships came into play recently, and the request of many other players like myself wanting to experience more pvp content from DDO than just bar fight I would like to suggest Airship PvP.
How this would work is that you can have the option to sail your Airship into a PvP zone. Once you arrive you will have the option of attacking other players, their ships, and securing floating islands for global guild buffs (20% hp or mana buff or something until the loss of the island).
Ships- Players can zone in and out of their airship when they choose as long as its in one piece and there is at least one live player aboard. Also one would have the ability to freely fly there ship about, move next to enemy ships to board it, and players can man the cannons to shoot at other vessels. Of course the bigger the ship the more cannons and hp it would have, the smaller the ship the faster it would be ( as to balance out participation among the smaller guilds). If a ship is destroyed it gets a 5 minute re-spawn time and can only be used to obtain buffs for land instances while in repair
Floating islands- These floating islands would be open world dungeons with traps, mobs, etc. Some floating islands would be more difficult to seize and in turn have better global guild buffs. Once a floating island is seized then that guild obtains a guild global buff, once that happens the instant resets, allowing another guild to try to attempt to seize it. Of course there dungeon can be interrupted by anyone opposing there push since its open world.