My thinking is that if the sale goes through, IAG ought to sell Dublin and Shannon more as gateways to the USA, due to the preclearance facilities. Does DUB have the capacity? According to the W14 Start of Season Report
here, pg 10, there's plenty of spare runway capacity 08:00-16:00, once all those early bird flights have left.
What about Terminal capacity? Mid-morning is when many US-bound flights leave already, and you can see that on pg 17 of that report: fewer flights but more Pax per US flight means that T2 in particular is quite busy mid-morning already - but still not as busy as early morning.