The LIRR M3s are in bad shape and break down a lot, doubt MN would want them or even need them.
Metro North would probably take extra dual modes before extra MUs. I remember reading a few years ago spare parts are getting scarce since GE stopped making parts for the P32, also low spare factor. If this is factual or rumor, I don't know.
The P32 was a good engine in its heyday unlike the LIRR diesels which were always kind of meh, but the P32s are supposedly starting to struggle from what I read a couple years back.