I can see Portrush area residents complaining that they were getting old trains while everywhere else got new ones (a fair enough argument it would be too), to be honest unless Translink was facing a rolling stock shortage (in which case it would be a good solution) there would be little incentive for them to do such a thing. After all, they would only be doing it to appease some enthusiasts, I'm doubtful that large numbers of them would use it regularly, while providing customers with an older (pushing 40 years) train while every other town on the system has one made in the 2000s or later.
I don't mean to be overly negative but such things would need to be looked at.
I think the only solution (unless people are happy to store one in a barn or something like that) would be for one to work on a preserved line. The problem then is, as pointed out by 4SRKT, is that there are no preserved lines on the same scale as the UK in Ireland. There is the DCDR, which is a very worthwhile project but on a smaller scale to UK mainland lines. The last time I was in Downpatrick I got the impression space is very much at a premium there, I don't know if it would have much commercial potential there either. Where else could you put one? In theory maybe someone with a bit of land could buy one and store it there statically just for the sake of preserving one. The ITG locos at Moyasta are stored on West Clare Railway land, though I believe there are plans to construct some sort of storage building there (permission for a museum building got turned down). A class A55 is cosmetically displayed in a pub in Castlerea.
So I think if an 80 class has any chance of being preserved in Ireland, people will have to come up with, and fund, some realistic way of storing it, maybe even going as far as buying land, etc... If not maybe it'll just have to be accepted when the last one is scrapped.
Sad but then again, it wouldn'd be the first time. Only four distinct GSR steam loco classes survived out of the many (hundred plus ?)that once existed (classes B1a, J15, K2 and J30). The GNR(I) the same amount (classes Q, S, V and that 2-4-2T in Cultra). Only three GSR built standard gauge carriages survive...two of which are minus bogies. The CIÉ diesel fleet seems to be the only one well represented in preservation (classes A, B101, B113, B121, B141, B181, C201, E421, G601/611, and, arguably, AEC 2600). As I said, it would be a pity no 80 class to survive (but at least there is one is sort of preserved in England), but it will be up to those interested to put together a feasible plan, with their own funding and rescoures if anything is to happen.