I'm guessing you could structure all your quests so that it spawns all the relevant pieces (NPC's, special objects, etc) to the right "Season World" at the right time
You could create a global that gets changed between 0 and 1 depending what season it is. Next, make an alias for all the different pieces of your quest. Then in the "stage 0" you can make two different "stage items", condition them to react to the global (one 0 and one 1). Now you have two seperate script fragments to use for filling your alias's. the only drawback i can see at the moment is if the transition between seasons happens while the quest is half way through

Not sure if any of that actually helped, just thinking out loud really.
I hope you do figure this out, it will be an brillient feature to add to your mod
- Hypno