Interesting perspective Tom, but considering ArenaNet has only one game under their belt and Guild Wars being it's first baby. I highly doubt they be comfortable leasing out another developer to add another expansion to GW1.

Part of me wouldn't mind another expansion, particularly one for Factions and another for Nightfall. Eye of the North was really a sequel to Prophecies.

Also I'm not concerned at all about the release dates, because these things take years to create, including the books. A good novel takes at least 3-5 years to write, lets not rush them.