What do you mean by “west of the divide” and “opened up”?
The continental divide: Some watersheds upstate drain west, others east. Some of those draining east, iirc, feed NYCs water supply, those draining west do not. (If I am wrong about that, someone correct me).
Areas west of the divide could be produced without any danger of surface contamination, however remote, of the NYC water supply, and that would likely remove most of the resistance to Natural Gas production.
New York may benefit in the long run by waiting, however, as the current boom has depressed Natural Gas prices. As an eventuality, the State might collect more in extraction tax from the same production if that production has a higher value.
In the meantime, though, areas where the pickings are lean will remain that way.