Heyas, i have some possiblities for your game
1. Static block damage. Currently blocks seem to have the same block damage situation like in minecraft. Like you deal a block damage and see the cracks in the block. After you stop those cracks disappear. Means the block has magically full life again. What about a static damage model which means the block keeps the dealt damage.
2. Landclaims: What about the possibility to implement (maybe later ;)) a kind of a claim. Possibilities are either a landclaim deed buyable from a (maybe playermade) kingdom or a kind of old landclaim where you set "claimstones" to the corners of you land. Possbile action are that you can enter who is allowed to "use" stuff on your claim, who can pick up items, and who can destroy stuff. maybe you could work with a friendsystem here where the player can choose diffferent group and rights. Also it could be possible to highlight the claim by rightclick or "use" the claimstone to see how big the claim is.
3. Playermade maps : Would be cool if player could "map" the world either by skill or by material. Like paper, ink, compass etc. The used map could be expanded and merged with other player maps to a big map. That way, cartography would be a recommended profession in the game and an advantage for every kingdom. Also its easier for people ot find each other