This is fantastic idea. I2P has this idea implemented. It is call grace shutdown. This notifies other nodes that the tunnel will shut down, so they will need to build a tunnel. Same situation, but different aspects. Replace tunnel with data. Sudden shutdown causes problems short and long run. Yes, we do need additional reserves to maintain the unexpectancy. Given a reason, nodes should be informed of what it is happening to the current situation. This gives future a change to cope the repercussion from the past. Maintain the order of the system.
Nodes should still given a chance to recover, and become a better node. Health should be assigned to nodes, like @neo stated. Another thing to add, class system is easier to maintain the order than free for all. If one plays rpg games, they would understand how each class system can effect greatly. One would be too strong, and others would be too weak. DnD is a great example. Dota, Dota 2, HoN, and LoL is another great example. Each character plays a role of certain classes to achieve great results. The biggest hurdle in those games is that 5 players has a choice to play a role, and if they choose the wrong role, it effects the entire game from start. 5 carries vs well balanced team. Who wins? Obviously the well balanced team. Balance team in team of 5 contains; Carry, ganker, supporter, crowd control, and tank. Lets further to expand this quest... Taking this idea and merge into safenet.
Ganker is a character who can set up ganks (raid), to tackle a problem, to delay the time, to give a team chance to maintain, and dominate the game. Ganker would most likely be used by cell phone users. Users most likely want to communicate, then disconnect. It cost them data for running it. Safenet requires more data than mobile towers.
Supporter is a character who heals other characters, and sets up wards to keep their eyes open of enemies. This is is a stage before the archive nodes. It already had good health, maintain the uptime, and keeping their eyes out on bad nodes. It actually boost for gankers, aka cellphone nodes. They are excellent users entire game. No matter what, it will always be useful even though it is weak. Weak meaning that gankers can get all roles killed if preform terribly.
Crowd Control is a character who manipulate the situation. Delay the carry from attacking, taking down enemies, move characters out of way, and so forth. They would be good for people who only wants to stay on for few hours or so, and will be disconnected for rest of the day. They hold data, then transfer it to another node before graceful shutdown. Gankers become weak in long run. That's wher carry comes to play.
Carry is a character who carries the entire team to victory. However they are slow at start, and can't do much. But at the end, it earns items that benefits the entire team and himself greatly, it can single handle change the game, and/or end it. The final stage before becoming a tank. These guys are hold enough to be archive nodes, but not enough to be one because they are not "tank". They can be taken out by gankers, supporters, and crowd control.
Tank is a character who can take a lot of damage, and still survive. This is the 99 percent uptime for nodes. They can withstand everything that comes to them. The general rule is ignore tank, and focus on any other character. They become the archives nodes.
So we have 32 nodes per cluster (bucket), and we got new RFC proposal which is split group, so there would be 16-16 nodes. Each of the 16 nodes plays a role. Each split group would contain each specific role that I stated above. From my perspective of things, I think cellphone users should be 8 per split group. There are more cellphone users than desktop users. Cellphone users cost safenet survival.
This of course will change when we have open source mesh networking, and professional code that doesn't take a lot of CPU resources...... Then cellphone users can actually become archive nodes.