So, I've been playing with this for nearly a week now. It considers pretty much every type of surface transport - options for train, tram, bus, coach, ferry, taxi and walking, although they're not quite sure what to do with the country's one cable car.
The planner is time sensitive, so that if you ask for a trip to the airport at 4am, you might get quite a different answer to the same enquiry at 4pm.
Aside from more than 200 rail stations, it has more than 12,000 bus stops, and 100,000km of roads. The real challenge is likely to be getting the data right and ensuring that all appropriate means of access are considered, so as to give the passenger the best options.
Depending on the journey, it normally returns about 4-5 train/tram/bus options and one taxi option or a combination thereof. It can plan a trip (admittedly a minority sport) from Dursey Island in west Cork all the way to west Donegal, although I have to warn you, it is a 15 hour trip.
Feel free to drop me an e-mail to try this out.