Just to pick up the point on ORK-AMS and ORK-CDG being alternatives to ORK-BRU. (I live in Belgium, I am from Cork).
Advantage of BRU-ORK for me versus AMS-ORK:- Save 3 hours travelling
- Save 80 euros in train costs (it's rather difficult to get cheaper than that for the trains I'd need)
- Save a half days holidays at work
Advantage of BRU-ORK for me versus CDG-ORK:- Save 3 hours travelling (There's no train service anymore between Brussels and CDG. Necessary to go to Paris-Nord first, then take the RER.)
- Save 80 euros in train + RER costs (cheaper is rare, more expensive is likely)
- Save a full days holidays at work
International train tickets:- You can only reserve 3 months or less before departure
- Train tickets cannot be mailed to Ireland
- You miss the specific train you reserved for (eg. due to a plane delay) and it costs and arm and leg and quite a bit if time to get on the next train.
For me, AMS/CDG are not such convenient or cheap alternatives 
SNN-London vs ORK-London would add* a maximum of - 2 hours bus (*Cork city to Shannon is 2h30 - Cork city to Cork Airport 0h20)
- 20 euro return bus fare (*Cork city - Shannon fare minus Cork city to Cork airport fare)
- Half days holiday at work
But I'm not suggesting there be no ORK-London/Malaga/Alicante/Paris routes and all traffic go via Shannon. Even if it is
"only" a maximum of 2 hours and 20 euros
extra to go via Shannon...
If the connections between Brussels and Amsterdam/Paris were so cheap and convenient then Aer Lingus could replace ORK-AMS and ORK-CDG by a 3-daily ORK-BRU
Okay, I'm joking. But I'm just trying to illustrate my point.
If this were to happen I don't expect regular passengers on ORK-CDG or ORK-AMS would be saying "Shur I'm not bothered, it's fierce convenient and cheap for me to get from BRU to my final destination in France/The Netherlands".
Also, that's the thing. Lot's of people travelling between Cork and Belgium are not going to Brussels, but somewhere else like Ostend, Bruges, Ghent, Liège, Leuven, etc which are even further away from Amsterdam/Paris...
It boils down to the question: is there enough demand for a ORK-BRU route?
I think so. So do the people from Cork who come to visit me. So do the 140+ people who joined that Facebook group, and their partners/children/family/friends who would also potentially use the route. And that Facebook group represents a small subset of all people wanting the route. And the existence of the route itself would also generate passengers who never thought about travelling to Brussels previously...
Okay others may believe there is not enough demand for the route. No problem. They're entitled to their opinions, and can try to convince me otherwise if they wish