Just stumbled upon this old post. Very good question, but very unlikely. Metro-North was formed in 1983. Metro-North at that time in its infancy, in my opinion, had its hands full trying to keep its inheritated lines running with the run down equipment which it operated. The FL9's were nearly 30 years old...while going through different rebuilds/or on the verge of rebuilding, they were showing their age. In Penn Central and Conrail years, these engines were held together as best as humanly possible, sometimes with plywood on their sides. To drain equipment from the Harlem, Hudson and New Haven lines to use on the Put would not have gone over too well with the majority of voters, who had existing patterns of commuting, stations near their houses and most likely would not want to change, again my opinion. To take on the Put would have been a money pit for the MTA/Metro-North. Much of the Put back then had tracks that had ties that were barely adequate for the sporatic freight trains which ran on the lower half at that time. I walked a lot of the Lower Put in the 1980's...To bring the track up to spec for daily passenger service would have meant a major tie replacement program. Don't forget that many parts of the Put had one track, not conducive for running a freight railroad, let alone a commuter line. Then, there is the "elephant in the room," the whole issue of no direct access to Grand Central.
I didn't even mention the NIMBY's with backyards abutting the Put. That would have been another battle. It took Westchester a LONG time to get some of that property back on the Lower Put by businesses and homeowners who encroached on the ROW.
One other (expensive) thing...most of the stations were long gone. Only a handful still existed. Money would have needed to be allocated in the MTA/Metro-North capital program for several years to construct new stations, platforms, parking, etc.
I grew up playing little league baseball in Yonkers and would hope for a lull in the games to watch RS-3's pulling their short freights going north...lots of fun while it lasted!
Tom