There is no way in hell EI are going to start TAs from either Cork or Belfast in the near future. Doing so would only take passengers that already travel from either Dub Or Snn. Why would you increase costs while splitting revenue? They did look(or more likely glance) at converting 321s, but the cost outweighed the potential benefit. Wet-leasing something like a 757 is allowed by employee agreements, but refer to point 1 again.
With the improvements in the Republics road networks I think it is unlikely that we will see ANY longhaul routes out of Cork or Belfast, nor any expansion of existing routes from Shannon in the medium to long term.
Next route we are likely to see is a west coast from Dublin, but that may be a couple of years away yet.