As a DSA forum member, who doesn't place much store by these rumours ...
On the one hand I can't see why it should happen. I would have thought Jet2 had enough going from LBA and MAN et all in the present climate but on the other ...
If they did start just 2 or 3 routes they wouldn't necessarily be competing with TOM in the same market. TOM are heavily into the package holiday while JET2 (correct me if I'm wrong) are predominantly flight only. There've been a few people around these parts asking for flight only flights just lately. Then again, making the move now the CATIII is in operation makes sense because I don't know how much a diversion costs, or how much they cost Jet2 last year, but it must make the operations side a lot easier knowing with much more certainty that the a/c are going to end up where you want 'em. And then again, if Jet2 are thinking of going transatlantic with a 763 or something then as well as pax I'm sure they'd want it packed with as much freight as it could take to make it as profitable as possible. Having a runway of DSA's length would give them that option without the need for a (presumably extra cost??) re-fuelling stop.
Having said all that, I still don't think it'll come to much.