There is zero chance of Jet2 buying larger, wide-bodied aircrafts and absolutely no chance of them joining the long haul market besides there winter breaks to EWR.
With the success of Jet2Holidays, it's slightly understandable why people think they could be successful in the long haul market. But maintaining long haul aircrafts, especially with Jet2 buying mostly older aircraft, I think it would be incredibly hard to make any money and fill these aircraft. There's no need for them to use them for places like SSH... It's wouldn't make any financial sense. I'm sure they would just increase the rotations.
From what I know, and what everybody else can see also, it's definitely not on the agenda and there's no reason for it too either.