At the same time, even though few people expect to make (or lose) much money trading the future there is still a liquid market?
If there is enough uncertainty around realized NGDP growth to generate a liquid market then there is enough uncertainty to create a hedging demand. This last paragraph addresses your point 123, in the inflation swaps market there is enough uncertainty around inflation targets being hit that you have trading BOTH for profit and hedging. Scott’s idea only works if the futures are traded for profit BUT NOT for hedging.
