Thank you everyone for your reply to this topic.

Yes, unfortunately, there most likely will be too little demand, also in the future. That's why it even says "will probably never happen" right in the subject of the thread.

Many might think that won't be the reason though, because getting to the airport for 6 a.m. departures is what many travelers do all the time. And probably it won't be necessary to get out of bed at 2 a.m. - most of the time 3 a.m. will do it, or even 3.30 a.m.

Seriously, most European airports start operating at 6 a.m., and there is bustling activity at that hour. This morning at Dublin airport alone there were 30 departures between 6 a.m. and 6.50 a.m. To many, it might not seem very logical that everybody else has no problem to get to the airport early, just potential travelers to Boston would.

All across Europe (and in Dublin as well), there are even hotels offering "Sleep & Fly" or "Park & Sleep & Fly" packages, probably just to cater to early morning flyers.

As mentioned above in the first post, if turnaround time was smaller, like f.e. if 2h 30mins was enough like it is for other airlines at BOS, Aer Lingus could even only leave DUB at 7.10 (or arrive back at DUB at 9.55 p.m., or anything inbetween).

This might also not be the reason, as there are already lots of early morning departures into the US, f.e. 7.30 from LHR to IAD with United, or 7.45 from LHR to ORD with American. The majority of people report it is pretty easy to adjust to the days being longer when flying westbound. Most of the times for most people, it won't be a jetlag that drags on for a week (which happens to some people when they fly eastbound though).

The main reasons a day flight won't happen would probably be that there are no onward connections from DUB, and that DUB (though being a metro area of nearly 2 million people) is too small of a market. But the sole fact of arriving late should not be too big of a factor, as the ORD-LHR day flight of American Airlines is also scheduled to arrive only at 10.45 p.m. in London. I took that flight myself, it was great, despite the fact that even the tube doesn't run anymore from LHR into the city by the time you collected your bags, even if it is on time, and often it lands late. Even in case it's not late, the last Heathrow Express might already be gone, so the only ways for sure into the city are a taxi or the N9 night bus. Despite this late 10.45 p.m. arrival, the ORD-LHR flight seems to be popular enough to fill a 216-seat B767, so if Aer Lingus even offered a day flight it could also be on an aircraft similar to the 177-seat B757 by Air Contractors, and probably not on a 272-seat A330-200.