I am definitely not doubting that Stansted could sustain a daily flight to New York it surely could along with a daily EK flight to Dubai but IMHO I think that any New York flight we'll be down to JetBlue 'if and when they announce transatlantic operations' which seem to have some relevance if you have read other aviation forums of late.
If JetBlue do intend flying JFK to London they would have no transatlantic competition at Stansted and it could feed it's New York JFK hub along with feed by Ryanair at this end.