The N Class will still be in use by vline for 5 years at least. They hung onto the P classes for at least 3 years after they stopped using them prior to selling the ones they did. I assume SSR presented an unsolicited offer at some point? Cant see them becoming available to an alternate operator any time soon. However, don't know how many N's one might consider "spare" given the nature of the timetable, and likely service changes over the coming 12-24 months. Will the SG sets go back to BG when Albury goes VLocity for example? or might we see services to new destinations? or those sets and locos mothballed?
Remember also that they are geared for passenger running, 115km/h i think. would re-gearing for freight, to say 100km/h, make any marked difference in their pulling power, and therefor effectiveness for freight, with the same power plant?
As for NSW, I believe several C's have been fitted with silencers to keep NSW regulators happy. One imagines the same could happen with the N's, with some HP penalty I would expect, to meet compliance there.
As for the alternative new double ended loco's, those Progress Rail ones quoted look to be setup for SG, and who's to say they are suitable for BG operation, and also are a bit heavy for the most of the victorian network. Any operator getting them will want something in the same load range as the G class. These progress rail locos are just one option however.