I’m not sure about code sharing with BA but I think Aer Lingus’ expansion might leave BA rather anxious as to Aer Lingus’ future as a partner. Consider this, all of BA’s Oneworld partners before the entry of Swiss, were on the boundaries of Europe (Finnair, Aer Lingus and Iberia) all serving niche markets for the big guys at Heathrow. The more they expand the less interlining that is needed with Heathrow. When they expand more to the US then this is just emphasised even more. Their reliance on Heathrow is shrinking, traditionally they always had pretty bad European links and so BA and Heathrow were of great importance. Now, well 28 new destinations in two years gives you your answer.