If "enough" miners don't require a fee, then some transactors will not send transactions with a fee, and many others will simply send insignificant fees (like now). Some miners that were mining for a profit will no longer be able to make a profit, and they will stop mining.
This can happen anytime now. Why would it be any different after the fork?
Despite what someone else claimed, this does not make confirmations take longer, increasing the price of transactions, and incentivizing more miners to mine, because of the fixed time to mine a block.
Either this will reduce the security of the bitcoin network, or stakeholders will mine "at a loss" to avoid losing their bitcoins.
And, it's silly to make stakeholders do PoW.
I still don't get how you go from Miners are mining at a loss to This is proof of stake.