I think it's a case of horses for courses; commonality is of no use or consolation if your main competitor can run rings around you when you're using the wrong airplane; don't get me wrong - there are a lot of positive aspects to the Airbus series and to the commonality not just between the A320 series, but the CCQ with the A330 as well. BUT ...
If EI is operating aircraft at very low loads on routes which could be sustained if they had a smaller aircrat and particularly, if FR is driving them out of particular markets, then it is surely time to think. A smaller jet which would (a) allow EI to maintain some marginal routes, (b) improve the prospects for having an effective hub at DUB and (c), most importantly, be more effective in challenging FR head-on makes a lot of sense.
Sean Coyle, given his FR experience, is in a very good position to understand the FR model and based on that, to draw up specification for an aircraft which could allow EI to tackle FR effectively on certain routes. Staying with the same model - either of business or of aircraft - when it's clear that it's not working, is stupid. All it's going to ensure is that EI will burn through its cash pile, for very little real gain - and that it is more likely to end up in FR's tender embrace.