There are very few options for further Jet2 expansion south of BHX, either lack of peak season slots, lack of aircraft parking, insufficient runway length, passenger caps, movement caps and night restrictions all limit the available summer programme new airport choices to EXT, CWL, BOH.
If current or pending planning applications are approved at LTN, STN, BRS, LGW and SOU, things might change, but none of these, if approved (far from certain), are likely to offer suitable new capacity in short order.
Meanwhile the established IT market is being increasingly pushed to long haul at LGW, the exception being the new EZY activity, which has yet to prove its worth.
There have been rumours of a BOH Jet2 base of 4-6 aircraft for some time.
Lastly Jet2 have recently purchased the TC slots at STN, BHX, and MAN. But interestingly not BRS, where EZY was successful. In my view that makes CWL, BOH, EXT more likely, my betting has always been BOH will be next and will be in 2021
FF