not sure if there is a format for server suggestions,   if so,  please inform.   But for now i'll just use the mod feature format

 Name of Feature: Chest locking!

Description: A new system for anti-grief!  it saves block space and Protects better than [Private]   signs.

When you place a chest it will automatically be locked,  this prevents it from being opened,  or hoppered by other players.  If you want other players to be allowed in you would hover your cursor over the chest and do /unlock.  If the player later changes their mind they can hover over the chest again and do /lock.   Likewise,  this would also work with hoppers, and furnaces and trapped chests.   However!!  if the hoppers,  furnaces and chests,  were placed all by the same person,  they would interact normally with eachother,  allowing things like industrial furnaces to be made. 

Along with being more secure,  this system would save resources and take up less space!  the minecraft chest has a latch on it,  so it would make much more sense being able to lock it instead of having to make place a sign on it. 

also,  the lack of a sign would allow for redstone creations like secretive  "slide away wall"  storage rooms

Any other information:    

This would only affect the Chest, trapped chest, hopper, and furnace,   unless it is decided it should be expanded to potion stands and anvils and the like.

Well, you could have it as a mod feature that way for all servers with DM they'd have this feature. That'd save stuff from other servers too. :)