IAG
In my view, this is a positive development. I see natuaral synergies between IAG and Aer Lingus. And contrary to comments, I do not see this as being an attempt by BA to gain more US traffic via LHR ex Ireland. The Ireland US network is strong, and will continue to grow. Dublin has potential for massive EU-US expansion. Like Dubai has, and we see even at airports like Reykjavik Icelandair, on the back of a very small population can sustain a great US network built on connecting traffic, Dublin has so much more potential.
The Dublin/ London route is a massive market, which is totally a focal point, why on earth would BA be a threat to that. What I could see is that larger aircraft could be used at a reduced frequency, that would make a lot of sense. Many of the departure times of BA and EI are largely complimentary in any case. Consolidate Aer Lingus' position on Ireland UK and release some slots, continue to grow the hub at Dublin.
The other benefits would be those of scale e.g. procurement and handling etc. Aer Lingus could bring its own strenghts to bear on the group operation and secure its future, which without a strong partner, could be extremely challenging. IAG is the right group for EI....