Did coal put a ceiling on natgas over the last few decades? Nope.
Yes,coal is affecting natgas short term because electrical generation is one of the ways natgas can be used without the infrastructure changes and/or large capital investments.
I was not writing about price ceilings - that's a tough subject esp. with volatile natgas. I was writing about cost floors. The full-cost of the highest cost dry shale gas needed to meet demand, and how that cost is $6 - $7 now, and will likely increase as drillers move from core to fringe areas of the plays.
I am mostly invested in 2018 - 19 contracts not because I don't foresee natgas hitting my $7 - $9 price targets before then, but because I don't want to take the risk of trying to time the market and I don't want to compete against HFTs and floor traders in rolling contracts forward in a market that is generally in contango.