SMP could use a "Cave Ins" type of mechanic where the player is required to put wood logs/planks around the area that they're mining in. If they fail to do so, then the blocks around them will fall then damage the player or suffocate them. I think this would be interesting to add to a future SMP server as it can make things interesting for the player. It can also limit the minimize the wood resources that players have and make it harder for them to mine for ores.
ChocoParrot created something like this before, but I don't know if he'd be interested in giving an updated version if any SMP Admin is interested in it.
Here's a clip of what happens:
ChocoParrot created something like this before, but I don't know if he'd be interested in giving an updated version if any SMP Admin is interested in it.
Here's a clip of what happens: