A crude calculation of UK population vs number of heritage lines suggests you need a population of 400,000 for each heritage line. Assuming that people in Ireland are as interested in railways as their UK counterparts, that means Ireland should, mutatis mutandis, have about 13 heritage lines. We apply some judgment to that and admit that interest is no more than half of UK. That gives us about 6 heritage lines or operations as a realistic figure for Ireland. So what do we have ?
1.Downpatrick
2. RPSI
3. Fintown
4. Kilmeaden
5. Dromod
6. Stradbally
7. Maam Cross
8. Giants Causeway
So by this very crude heuristic , we are at capacity already