Glass cockpit upgrades have been on the cards and rumoured for a long time, this IMHO does not change the plans for fleet renewal, the aircraft are just being invested in one last time to make them compliant with EASA regulations. The some -300's and some 757's will see another 6-8 years service.
Remember, it will take time for Boeing or Airbus to deliver aircraft, the existing fleet needs to continue operating during this period. I have no doubt that Jet2 have been in talks with both parties for a long time and will not announce or sign anything, until the deal is 100% in the best long term interests of the airline.
More -800's, for sure, they will keep expanding in a cautious way, as they have done over the last 5 years or so.
A330/'s I have no doubt, will appear for next summer, the demand is there, but long haul is a long way off IMHO.