It is my understanding, miners have the option to not upgrade, to upgrade to a different node and a different DAA implementation.
The problem is coordination, because without coordination there can be an unwanted chain split.
He tells he will not build blocks larger than 2 MB and other miners do the same.
If you look at the projected scaling, 4 MB are just few days later.
And, remember it is a soft fork, so it need the majority of the miners to orphan the >2MB blocks.
If BIP148 start and take every SegWit voting miner, it would start with a 35% hash rate (blocks every 30 minutes). Queues and fee would skyrocket pretty fast.
At the same time, EC miners (currently 40% going up), would become the majority of the hash rate (40% of the lasting 65% is ) and would fork briefly after to bigger…