The center of the map - summer never ends. Top and bottom - winter never ends. Gradual change of the duration in between.
Or maybe top - winter, bottom - summer.
I just remember Darkness in Salem and how hard it was to live there. Winter can serve as such environmental pressure. If you want to live alone - welcome to the north
Maybe generate a map the way that this is rewarding in terms of underground resources. It opens a lot of possibilities. For example, it can bring people closer together but will keep the world as large as it is or maybe even larger!
And it will end the season complains
This is probably a world resetting change, but i believe it will bring a lot of new things and will be very interesting.