I agree that minigames and interactive objects are always a great thing! It's definitely our intention to add the piano to the new version, actually we've already done some preparations for it, so it should be ready soon 
Back then for the Java version, it was also our intention to add some other games like chess, card games and smaller video games (similar to games like space invaders, pong etc). In multiplayer, you could even play these games with other people. We've done a few preparations for that, but unfortunately it never made it into the game... however, we still want to add that to the new version (but it has a lower priority at the moment) 
I very much like the metal detecting idea
It's definitely on our to-do list. The whittling suggestion also sounds interesting, we just have to think about how this could be implemented. We also have to think about the whistle idea... it sounds interesting, but it could be a bit overwhelming for the player if he gets too many "whistle-options" 