Monarch proved a demand last summer with a more leisure orientated frequency and timings - perhaps the price they had to sell the seats at were just not sustainable, but they certainly put bums on seats. Perhaps Jet2 might look at the route, operating on a similar basis to that which Monarch operated.
Nice idea, but a bit of a long shot. Vast majority of units head south, not north (unless you count the return leg...)
If they did, they probably try LBA/MAN first, as they do with LRH/EGC. With that trial in the 1st year, it would be bare minimum 2020 before they started from BHX, plenty of time for others to jump on the opportunity.
Having said that, Maybe Jet2 need to have a bit more faith in BHX? would certainly help diversify their portfolio and take advantage while they can