Disagree. Coal prices are driven by Chinese demand - their inventories are bulging and electricity demand is stagnant. Coal inventories are also bulging in the US as many power plants had take or pay contracts even though it was cheaper to burn natty. If natty hits $4, then most natty powergen will disappear and 3-4 Bcf demand will disappear creating significant pricing pressures as inventories begin to build.
To compound matters, $4 will cause significant resumption of drilling by desperate natty producers looking to generate cash flow.
Reality is $4 is upper limit for natty - and $2 is the bottom. Will roll back and forth until meaningful LNG export capacity is built - a decade from now. As such, will remain a horrific business.