I'm pretty new to this game so far been loving it!
Having a climate system would be interesting as well as a season system maybe inspecting cloud patterns and such.
Winter could affect the character if they lack proper clothing or make farming difficult maybe snow storms having players plow their affected areas.
day and night can also affect the different appearance of animals and such.
but yea it'd be cool to see something like that or maybe just frustrating to some but I love me some challenge!