Just a thought re the 100 seater discussion....
Yes I agree that an aircraft with that sort of seating capacity would be a nice to have but the costs are just prohibitive for Aer Lingus at this stage. I've seen an airline try to introduce new aircraft of the same type but with different engine type and honestly it just eats resource. If you now throw in a different airframe and crew training etc., it is a significant investment and I really don't believe EI can justify it.
The A319 is a good airplane also but I'd be interested to see how it compares to the A320 on a cash operating cost basis i.e. do the disposal costs of A320's justify the acquisition of A319's? Also, bear in mind the EZY A319's are effectively specials with the double overwing exits which allows them increase the pax numbers to 156 (18 less than an EIN A320) from a nominal 134 (40 less than an EIN A319). The sales figures for the A318 speaks for itself and on that basis, I don't believe you'll ever see it in the EI fleet.....unless they are being leased in at US$0/month.
With regard to the A350's, I think they should go for it but the A350-900 is too big, a better choice would be to exercise the options and switch to the A350-800. The seating capacity better matches the current A330 fleet and ultimately, the A330's will have to be replaced with something. I know the 350-800 isn't an optimal airplane (heavy for it's size) but there's limited scope out there for acquiring other A/C. The B787 is probably a better match to the requirements but you'd lose out on the cockpit commonality which has significant benefits in an airline the size of EIN.
All the best,
P2C.