A330 @ Ltn
Yes Monarch have operated their A330's from LTN...
They use to fly a weekly charter on behalf Airtours flying Luton to Sanford non-stop. The route flew for the summer of 2001 and Airtours were very pleased with the loads and were selling tickets for summer 2002, but after the events of 9/11 and the decline in the industry the route saw the axe.
The route was restricted from Luton with a payload of 340 passengers and other than baggage, cargo on the flight was very restricted.
So in theory an A330-200 in three class config with about 220-250 passengers is possible on a 7-9hr mission. The chances of a legacy carrier operating this sort of route from LTN is very questionable?!
I think the only long haul routes likely from LTN, in the forseeable future is a start-up LCC. But this then goes back to the question of the runway, as these sort of airlines want to operate aircraft in maximum dense config. Or if we were really really lucky maybe a Continental 757-200 flying LTN-EWR or an Emirates A330 LTN-DXB.
(But I think I am dreaming!)