I've always wanted to do this I just don't have the coding abilities and I wish to learn them but here are some ideas
. Falling trees with animation
. Better graphics
. Electricity (solar panels, different cables, turbines, geothermal generators, conservator belts)
. More realistic crafting and recipes like crafting swords with anvils melted metal and cooling them etc.
Just a thew ideas but. Have plenty more if its possible for you to contact me about maybe giving me some tips to begin coding and creating or helping you in making a game like this