Paris would be out from Shannon as between Ryanair and Air France, it's a saturated route.
Amsterdam would be totally dependent on a KLM code share. I still haven't worked out why this never happened for Belfast.
The other problem with Amsterdam is that it would require basing an aircraft there or doing a W pattern. The first would mean you'd need to find a batch of other routes; the second would mean flight times that weren't ideal for intercontinental connections in Amsterdam.