Has IE ever transported milk? Not sure if they have the right stuff for that but anyway. As Noel said the main traffic was agri which would have decreased even though there can still have been traffic for it.
The GNR railmotors? I believe they were built by the north British locomotive company. As you said Bagnall built the WCR tanks which ate coal and unsurprisingly were bad steamers. So after that I think Bagnall didn't get many Irish orders after that
I would say it keeps going much further as I remember seeing what I believed was the line, at athlone, cut off just where a level crossing would have been
There are good quality 3d printers but they won't come into commercial affordability for maybe 10 years. I was watching a programme and they were even researching how to make printed organs!