I think the main reason they put a 763 to DUB and a 764 to SNN is that the 764 is still in "domestic" configuration, with a domestic first class and this is why, like AC, this is sold as an all-Y class flight. DUB would have a strong Business Class market and J class pax would more than likely not accept this product.
I see Michael Broughton, BA's chairman, is quoted in today's Indo as saying Open Skies might be as much as seven years away. Of course, you have to acknowledge that BA has a vested interest in Open Skies NOT happening - despite whatever else he says - because that will mean they'll lose the stranglehold on LHR. So, BA is more than happy with the current situation; as long as they can get the Americans and British squabbling away for a few years, they're happy to let them - and throw spanners in the works if they look like they might be close to agreement.
From an Irish perspective, the prospect of another seven years of the SNN stopover is simply not an option; either the EU will give us the green light to go ahead with a new bilateral with the US, or the govt should look at the possibility of opting out of the process altogether. When the EU took over negotiating rights with the US, never was it anticipated that something as peripheral as US airline ownership - irrelevant to most EU carriers - would be the sticking point.