The latest 6th August updates to the Jet2 page on PPJN are highly suspect, with some possible plonker-pulling as Chesty points out. I am doubtful about the AirTanker thing but don't have enough knowledge to confirm or deny this. The 757s will certainly go beyond 2020 and there definitely wouldn't be a 5 year bond for anyone transferring to the 737!
Someone with the know-how (or login) should edit the PPJN info and get rid of that BS.