Since you are not meant to kill other players in NonPVP areas, I feel there should be a change to anvils somehow. I was testing stuff with other players that included what you could where on your head, or things that could hurt other players, and we found out that you can hurt other people by dropping anvils on their head. I don't know how you would fix this, but I just wanted to let you know.
A 14 day War period on smp, where you can make alliances, declare war, and defend your territory. There would be a power system where if you had more power than another player you could overclaim their land. (So basically Smp and Factions combined)