Hey, that's a fun and relaxing game!
I saw you're planning to create a shop, it would be nice to receive some explanation at the beginning about how the wall crumbling works, I took a while to realize that bar at the bottom. I also didn't understand why I would use the pickaxe if the hammer is much more effective.
I also didn't understand the point of that metal parts.
I don't think the game needs more modes, I'd just add harder rocks, and upgrades to the current tools. Maybe some enemies, or bombs that will cause it to crumble faster?
Some purchasable boosts to start the game with a sensor or something like it, to make the player spend some cash before starting the match, without knowing if he'll recoup that value.