Psi, Alexis, please note that looking at just the permeability...

Psi, Alexis, please note that looking at just the permeability is not necessarily the way to go. It is actually the permeability times height that dictates to a large degree what production is. In other words, kh. From this one can understand that increasing the thickness from 5 meters to say 50 meters will increase the potential flow rate 10 fold.
The other issue raised was the swelling of the coals due to pressure depletion, fractures closing. True, but coals actually may show shrinkage as it loses gas molecules as fractures open up. Which one will be the dominant one, decreasing the permeability or increasing it over the life of the well/field, is a matter of a lot of studies and discussions, end result depending on a large number of coal and fracture parameters.