There was an agreement in principle to bring in a Bus / Luas / Commuter rail add-on for point-to-point tickets in last November's fare determination. They acknowledged that it was going to be difficult to implement so it might be next year before it happens.
The whole rail-only nature of point-to-point tickets is just silly. There are two expressway busses heading through Mullingar, Edgeworthstown and Longford after the last train and it would make perfect logical sense to be able to buy an add-on to get access to those busses.
I suggested this to the NTA a couple of years ago but you might as well ask to be able to take a sub-orbital rocket to Longford since Expressway is a "commercial" service.