Focusing on the Dublin-Boston proposal, the first obvious objection is that Aer Lingus are already operating that route aggressively. This new fare would need to be
really good for passengers to accept an alternate airport such as Manchester NH or Hartford CT.
I'm wondering about this "secondary airport" that Dublin apparently has. It can't be Casement (
EIME), can it, at just 6000 ft? Apart from that, the only long runways outside Dublin are Belfast and a couple on the other side of the country: Shannon (11,000 ft) or Connaught (EIKN, 7,500 ft). (According to
World Aero Data, that is.)