I always, personally, wished a mmo would have seasons, they could be longer or shorter than standard RL seasons but it'd be fun to have a periodic change, maybe going from fall to winter while the game is down for maintenance. Or perhaps, since many games have monthly down-times, a more subtle change, leaves turning slightly in Sep., a sea of orange and yellow in Oct. and then falling leaves/bare trees in Nov. onto snow in Dec/Jan. and then the snow ending in Feb etc.

Or just a quarterly change and have four basic seasons with less than subtle changes. It would be an ideal but it may be hard to do each landscape and recolor/edit 4 times per you know? Always wished for something like this, could you imagine Gridania with all the leaves a beautiful orange or vibrant yellow?