Unfortunately, this is another case of the heart ruling the head. Neither the northern or southern administrations have the money for these schemes. The fact that the trackbed of a former route exists undisturbed is zero reason to put it back. There would have to be a sound business case. Freight will simply not just appear, nor passengers in Luas-style numbers which would make the thing self supporting. The trend in western societies for the last fifty years, and likely to remain, is to lighten the load on public purses to reduce tax. The capital costs of these schemes would be cheaper per mile than motorways by a long way, but that's not the way the public and their elected reps will look at it.
Scemes have been suggested to reopen the Valentia line, on the basis that if you just buy an "old steam train" and run it, sure it'll make a fortune, so it will. Same for Buncrana, and the various manifestations of a Great Derry, Barnesmore & Sligo Railway.
Nice to think of, and who knows, a model railway based on Sligo to Derry via the SLNCR would make a truly fascinating project, but that's about it. Therefore, it's probably most appropriate to discuss such a new railway to Enniskillen on these model railway based boards, as opposed to public meetings or even the IRN!