OK, it ain't gonna happen, but the game has slowly been gaining "seasonal" changes for things like pets and fishing. Zones, however, tend to be frozen in the season that they're associated with -- even where there are seasonal changes for something like pet spawns. Seasonal changes would mean altering whole zones and creating multiple looks for each zone, so I'm pretty sure it would be one of those projects that get a nod as possibly cool but too resource intensive.
On the other hand, I'm curious. Do you think seasonal changes would add to the game, be a distraction, be an outright annoyance because they'd change the look of a zone, or do you simply crave pizza quattro stagioni now?