In all fairness, BA were mugging people for MAN-LGW returns before Jet2 came along, and it was inevitable that someone would have a go at the route before long. However, Jet2 have made a pretty fist of it - awareness of the route at the Gatwick end is virtually non-existent. Some advertising in North Terminal to attract the BA customers might have been a good idea, but none has been done. Add to that the cuts in weekend flights, often required by airlines to move pos crews back and forth, and it is not a good recipe.
If they do pull off, it will not be a surprise. But one can only hope that BA increase capacity slightly instead of just racking fares back up.