Absolutely adore this game and it has firmly become my favourite game of all time.
I had a few ideas, which have most likely been suggested before or already thought of but just in case here they are;
Vehicle build including; dirt bike, box racer, paddle boat, enhanced glider, paper aeroplane.
Weapons including harpoon, flaming arrows.
Ability to dig moats or tunnels.
Ability to build adventure park features such as climbing frames, slides, swings etc.
Animal development including squirrels or bury nuts that you dig up. A bird house with smaller birds who have a field of view area that will lead to them eating you if seen plus drop bird seed. A grass snake that leaves skin sheds. A frog that jumps from lily pad to lily pad. Cat/ dog shedding/fur ball/ biscuits.
Allow base pack and rebuild I.e. ability to move walls, roof, floor etc.
Introduce lifts and escalator builds on pull system.
Introduce vines/ veg patch for additional resources and climb.
Ability to have larger bugs to use as defence and travel.
Offer local split screen coop play
Online open world concept allowing for tribal battles.
Create own avatar/alter outfits of characters.
Introduce weather to the game.
Garden features such as gravel/shale/decking areas.
Garden gnome or washing line lab entrance to new biome.
New bugs including; Worms, moths, butterflies, crickets, earwigs, centipede, ticks, fleas, wasps, hornets, daddy long legs/crane flies & blue bottle fly. Not to forget a queen bee.
Hiking gear to climb walls( could also be solved with vines.
Lastly open the house and shed up but that one is the most obvious of them all .