How we could use demurrage fees as transaction fees and what benefits this would bring:   Theoretically it would be possible to use the demurrage fee as transaction fee. This could look like this: In an given block a part* of the block-reward is assigned to transactions as additional paid fee*** according to how much demurrage they pay (similar to coin age the transaction destroys).  This could be implemented as soft fork. This would help also to reduce that transac