Technically, it is up to each node operator to set the
minRelayTxFee as he pleases.
Assume a transaction with less than 1Sat/vB in transaction fees and a fairly empty mempool.
Is it possible to identify nodes on the network that are likely to forward or have previously forwarded transactions with less than default minimum fees?
If a subnet of such nodes existed, miners should be incentivized to also connect to it -- at least in times of empty mempool.
Originally, I did not intend to discuss my assumptions about miners' incentives. However, I find that discussion rather interesting, and will happily clarify my views.
I understand that close to zero fee transactions may (currently) not incentivize miners enough. On the other hand, we can be certain that in principle miners are willing to include transactions at a fee of 999 Sat/vB. That being said, I think it is a fair assumption that a market price could be established somewhere in between, i.e. 0 < fee < 1000 Sat/vB. If that is true, transaction fees currently do NOT represent a market price, due to
minRelayTxFee = 1000.
Furthermore the incentive to include non-standard transactions is likely to depend on the fiat price of Bitcoin, as the labour necessary for a transition is likely to be priced in fiat. I conclude that the incentive will grow in the future.
Finally, I do not agree with the notion that the demand for transaction is flat (static, fixed). I am absolutely certain of a demand for cheaper transactions.
Regardless of the transactions miners receive, nobody can force them to include those transactions in a block anyhow. If miners regard transactions as too cheap, they may very well omit them. It may not be wise to do so, because the fees, as little as they may be, will be picked up by another miner. Miners (i.e. some miners/a miner/somebody) will eventually change their parameters if the volume of non-standard transactions becomes large enough.
My entire argument is about extending the fee market to the lower side.