I would like to see a STN-JFK think it would be very popular
So would I but not with TCX. Not that I have anything against them, quite the opposite, but STN really does need a regular (ie daily, year round) full-service carrier to JFK/EWR to operate at its full potential.
I'm sure TCX will continue to grow long-haul at STN, judging by their increases next summer and how well they've sold this year.
It does seem that MAN is where their long-haul ambitions are focused but who knows? It's another one of those cases of wait and see I think.