As somebody who appreciates transatlantic day flights like those offered to London, recently I realized Aer Lingus would be able to offer the same service, and even without the disadvantage of losing roughly a day of aircraft utilization. For example all the existing offerings to LHR, no matter whether by British Airways (BOS, JFK), Delta (JFK), United (EWR, IAD), American (ORD) result in an operational disadvantage for the airline as the flight leaving the US in the morning and arriving in LHR in the evening lead to the aircraft not being able to turn around quickly and continue with another transatlantic flight, it's realistically not feasible on either end.

For a possible Aer Lingus Dublin to Boston service, things would be different, with an early morning scheduled departure in DUB f.e. at 6.00 a.m. (with actual take-off normally happening a little later, because of US pre-clearance), arriving in BOS 8.05 a.m. after their usual 7h 5mins scheduled flight time. The turnaround time at Boston for the late afternoon B757 usually is 3h 40mins, meaning in case of leaving f.e. BOS 11.45 a.m. the flight would arrive DUB 10.55 p.m. (22.55) after their usual 6h 10mins flight time. Not being aware of any curfew at DUB, it would technically be possible, and the Dublin departure could possible be later respectively return arrival possibly could be even earlier if it was feasible to plan with a shorter turnaround time.

Of course Aer Lingus very likely won't be doing this, as their focus is turning Dublin into a transatlantic hub, and the day flights won't be able to offer any same-day onward connections. At the same time, day flights always do have advantages, and in this case the "Be the first to land in the US" could be attractive f.e. to business travelers, who could easily go to meetings later in the same day, especially as pre-clearance already took place in Dublin. At the same time, the dayflight back to Ireland f.e. would allow travelers to still go to make full use of the next day after previously sleeping in an actual bed - after all, the London day flights are also popular. Still, despite strong Irish-US ties, Dublin would probably be too small of a market for sufficient demand - still at least Aer Lingus could possibly operate it with better aircraft utilization...