Before the rumour mill kicks into full force, it should be pointed out that these LHR plans aren't confirmed. Aer Lingus are currently bidding for the slots that BA were forced to release as part of the conditions set down by the European Commission on them acquiring bmi. But, Virgin Atlantic are bidding for them as well and have plans to develop a new domestic network in the UK. The slots in question are for specific routes, so Aer Lingus would be forced to use the slots for those routes and not to Ireland.
No doubt Etihad's thinking is that if Aer Lingus get the slots, they can code share with them on flights to Abu Dhabi from Heathrow, providing feed for their own hub. So assuming this all plays out, it'll be interesting to see what BA's reaction will be to Aer Lingus. Will they see it as a threat and end the Ireland-UK code share?