Viable to run to Vernon: Yes - 90% of commuters here commute to the immediate metro area (I.E. Bergen/Passaic/Hudson) or NYC + reverse service during the day would take traffic off the roads.. Especially during the winter months.
Viable to run on intersection of 515/23: Yes - Currently they have installed a park and ride in the intersection of 515 and 23 on the parking lot of that restaurant (whatever the name is.) It just happens to be along a stretch of the NY&SW line. Lot is full every morning and commuting on 23 since they put in that park and ride seems to have gotten better.
Major NIMBY opposition only exists in Sparta. I actually took a drive through that area and I do see why they dont want passenger rail service. The majority of the town is full of mansions.
Outside of Sparta, you'll encounter supporters for the project. Vernon is the equivalent in terms of population and type of income to Sparta. The one difference is that people here are smart and know that rail service will benefit the area.