A single auction house, so everything's in stock, and the price for goods tanks because of competition.
Camps become overcrowded, thus leading to a need to change the size of each group for xp/cp; and increase in the quantity or lowering of respawn for item camps.
shouts/yell turning into its worst form possible. I see nothing wrong with this.
Instance overcrowding to the max, leading to the need to cannibalize old servers for more instances.
People from other servers will be pissed about having to change their names; so to eliminate the joy of those on the original server add a number to the end of everyone's names.
Not enough crafting competition from combining all 16 servers? let's lower the difficulty of finishing the final stage of the shield a bit, so whatever profit margins existed for having one goes down the drain.
Gotta give these masochists what they really want. Suffering followed by a reward long past its expiration date.