Allow user defined fees. Incentivize paying higher fee with a fee token.
hypothetical:
paying zero fee, requires POW upto minimum 1 BTS, no fee token issued.
paying minimum 1 BTS fee, no POW required, no Fee token issued.
paying more then 1 BTS fee upto maximum 100BTS fee, no POW required, Issues user a fee token.
The fee token could be used for various things like reputation, discounts, sharedrop, dividends, referral bonus, lottery etc? What other incentives could there be for voluntarily paying higher fees?
Maybe the fee token gradually degrades over time, but can be used instead of BTS to pay fees at a discount. So initially you elect to pay 100 BTS fee and receive 200 fee tokens which can then be used to pay fees for some amount of time at a discount.
just some random thoughts.