In 10 years I think Jet2's fleet will probably look something like:
Majority 737 800's, 20-30+
A few less 757's than now, but still 8-ish
Substantial fleet of 737 300's, specifically QC and wingletted, 10-15
Large fleet of either 737 700's or A319's, 10-20
Subfleet of A330 200/300's, 4-6
Probably around 75 aircraft in the fleet
738's are flexible, they can operate city routes, sun routes and longer routes and are the perfect size for LS' operations, they make more sense than the -700's however...
If LS want to keep up the cargo, I believe there is a 737 700QC? But not 800, so unless they struck a deal with Boeing to do some 800QC's for them then LS will run the 733's into the ground and will be more likely to go for the -700QC despite the A319 probably making more sense... I don't think Airbus will be in the market for converting 5 or so to A319QC's
757's will be a real problem to replace for Jet2, A321's are the obvious option but the older A321's which Jet2 would be buying couldn't do the canaries from NCL, LBA and would probably struggle from GLA too... I think we'll see at least 1 LS 757 flying around somewhere in 2030.
A330's will be used mainly on routes that used to be operated by 757's but with a reduced frequency and probably alongside 738's, probably for SFB and CUN as well.
Wish LS the best of luck, I'm sure they know what they're doing