Does Bournemouth have the same draw (ease of use, transport links, pleasant and efficient experience) as Southampton for the Southern, wealthy Home Counties contingent?
I do believe in "build it and they will come" and Bournemouth could take a Jet2 base of desired size with any of their current aircraft types from day 1 without additional considerations being made however an established BOH base would negate a future SOU base should SOU become suitable.
I personally couldn't see Jet2 entering any new market with less than 4 based aircraft and given the catchment area, I imagine any prospective South/South East base would have to have scope to grow to a similar size as their newest bases at a similar pace. What's that? 10 A/C+ each for Bristol, Stansted and Birmingham. That's most definitely too much of an ask for Southampton currently and technically feasible but a tall order for Bournemouth. I imagine the morning rush with more than 4 aircraft would be a thoroughly miserable experience at both airports as they currently stand.
I would love to see a sizeable Jet2 Southampton base... But it strikes me that the required work would be too much.