There is just no sustained demand to other destinations in Ireland.
Shannon would only work if, like many have said before, it tied in with a westbound transatlantic and could take advantage of the pre-clearance of customs. If they won't do it with Dublin you've little or no hope of Shannon.
Galway is a shed and last time I flew in there there were only Aer Arran flights to Luton, Manchester and Newcastle. Incidentally, the flight arrivals board was a Powerpoint slide which was quite amusing with some of the sound effects and swizzy animations they used for a lark one day to pass the inane sense of boredom.