It's impossible to say really, I was looking at the 'what might have been thread, have this:
I wonder what you'll think:
I too like to theorise on alternate timelines. It related to the development of the GNR Diesel Locomotive fleet. As you may be aware, it was constrained by the size of Dundalk Locomotive works, so they needed a 1,000hp B-B Diesel Hydraulic with a 15tonne (60 tonne total) weight, with a length of 39 feet (*12 meters). It was also to be Double ended, designed for mixed traffic usage.
It looks like one of those odd things with Ireland in that it is a broad gauge railway system, with narrow gauge axle load tolerances, even on something that I thought was reasonably well built, such as much of the Great Northern. That actually does not look like it was the case, and consequently explains its early closure in 1957.
There's only really one kind of machine that fits the bill, and it's in Thailand, built around 1964.
So if anyone wants to fire away and post what I've said, or speak to the other former users at IRN and what not, tell them what I've found.
As for what survives, we will always wonder about 'what might have been' when it comes to the big swathe of closures that occurred in 1957/1965. If it's got lots of level crossings, switchback gradients and speed restrictions galore, it just won't make it into the 1970s. Portadown to Derry MIGHT, but when it closed it was in the same condition as the Sligo or Rosslare lines in the 1990s. Portadown to Enniskillen, Enniskillen to Omagh can. The rest .....axed.
This rather compact neat looking machine could be the Great Northerns Mainline Diesel Hydraulic. What would it become under CIÉ? A 241 perhaps? Like other Diesel Hydraulics, I doubt it would last 20 years.
http://gallery.rotfaithai.com/categories.php?cat_id=25&sessionid=l3v2mmi7ps5b58l7ipgrj199j3