Another thought.

From Decrits, I got the idea of using transaction fees as a proxy for GDP. In a corner of the blogosphere, targetting a level path for the nominal value of GDP is being talked about as the correct way to target the money supply of an economy. i.e if by a certain time, nominal gdp is not as high as the level calculated by the growth path, then print money. If it is more, then withdraw money from the market by selling assets.

I, personally am in favour of such a policy for statist monetary policy. NGDP does look better than inflation targeting or money supply targeting.

So, a policy appropriate to crypto currencies could be to target a steady growth in nominal transaction fees. Have an initial booting up period where anyone who can bring in a certain amount of hashing power, brings it in and gets coins. It is a pure mordor coin during this initial period. After that (2-3 years, maybe, anybody have any ideas on how to determine when a crypto currency has stabilised?), the targetting mechanism takes over.

If the transaction fees paid in a certain interval of time (maybe a week or fortnight) exceed the level target, then automatically lock up a percentage of the money in every account. Coins that can be used now, lets say block height 99, get locked so that they can't be used till block 149. Ownership is maintained, but usage is constrained
 
If the transaction fees paid are below a level target, then automatic unlocking of locked coins occurs, Coins locked till block height 140 get changed so that they can be used in block 90 and so on.

The level target for transaction fees could be a linearly increasing one, exponential or sigmoid.