I have started diamond mining on smp3, after finding a village about 3,000 blocks from spawn. However, the only problem I've found is that I cannot move my diamonds to smp2 (where I have my res) without taking an hour to go back to town. This would be much easier if I could simply open my vault in the wild.
the problem with allowing opening the vault in the wild is that it will simply become a "Death Chest" Where the player would just load it up while they are out mining/exploring and then they die, but guess what.. they still have all of their stuff. This completely defies the purpose of a Survival server, if survival is no longer a threat. Where as your intentions may not be to do this, other people would abuse it. There is no question. And it would cause problems.