Looks like nothing is going to happen for at least another 2 years. Surely some sort of low-cost patch up of the 2700s could keep them running for 2 years which would alleviate the situation somewhat.
Overcrowding on the later morning Sligo services seems to be getting quite bad lately. A friend ended up standing from Edgeworthstown to Dublin a couple of weeks ago on the 10:30 ish service and another passenger said that she'd been standing from Carrick. Booking is no help with nobody to enforce it on most trains but at least you get a free journey.
There doesn't seem to be any good solution. Adding 41 cars to the 22Ks is also less than optimal since you'll be adding new cars that can't be used independently of units that will be up to 16 years old by that time. Based on Irish Rail's record, they'll be looking to get rid of the 22Ks by 2027 or so.