As for the buried treasure idea.
Instead of digging up leaves (furniture) or bells. Maybe you dig up treasure chests, and like how you take fossils to Blathers to get them identified, you could find a NPC (Pascal?) on the island and he opens up the chests for you.
GOD THIS BETTER HAPPEN!!
I'VE BEEN ENLIGHTENED ;D
I would also like a little shack where Kappin sells swimsuits and offers boat rides.