Community Center being used after it's finished! Other than Clint watching the furnace. Have Caroline and the other women use it to work out, have Penny teach Jas and Vincent there, have Leah teach people how to paint, sculpt, etc.
Let the farmer have a birthday! People will give you better or worse gifts depending on how many hearts you have with them.
Let Jas, Vincent and any children you have actually grow up.
Have characters like Maru leave for college. They can always come back, but leaving for a couple of years would make things more interesting. I never want to marry Maru because it feels like I'm holding her back. And yet she still stays at Pelican Town even if you don't date/marry her. Have Sebastian leave for Zuzu City, doesn't have to be forever. Can just be for a while. Have the characters date/marry each other, instead of waiting for the farmer to date them. Let them have children of their own, etc. Though that might be too big of a change.