the objection here is that txn data is meaningless. You can easily fix this by imposing a 0.1% tax on txns. Suddenly tax collection volume becomes a meaningful measure of txn volume. You need a tax like this anyways to keep mining sustainable. Two birds with one stone.
I was thinking in free transactions. But I guess that could work.
I still think that you can keep mining sustainable with demurrage, maybe even only with voluntary fees.