yeah, it would add some great replay-ability to the game.
things that are a must for seasons, most have already been mentioned:
seasonal crops, foragables, animals, fish
shallow water freezing (no clay in winter, no shallow water fish)
walking through snow reduces max run speed by 1
temperature mechanics
tree products/visuals determined by season
--- tree growth rate determined by season
seasons which last 90 ingame days
new worlds should start in winter (personal opinion)
in addition to all those features, I would also like to see
dynamic weather: snow, rain, thunderstorms, snowstorms.