"Might-have-beens" in preservation are very numerous!
Given willing manpower and money (neither existing in sufficient quantities in 99% of Irish society), anything's possible. I am aware, however, of several which were comprehensively researched, but nothing ever came of them. A section of the Tullow branch, a stretch of the Athboy branch, and a stretch of the erstwhile SLNCR near Belcoo, were all looked at in the 1990s / 2000s by several groups, and dirty tears ago the RPSI considered the ex-GNR Banbridge to Scarva line. The Fenit and Loughrea branches were in the preservation sights for a short while, and short sections of the Achill and Clifden lines were examined for possible preservation many years ago.
Imagine a comprehensive Festiniog-style section of the CDR; maybe Donegal to Stranorlar, and a good stretch of 5ft 3 as well. Banbridge would be quite ok! Or a scenic part of Mallow to Waterford..... Achill would be excellent....
Too many possibilities.....
Several narrow