Easyjet pilots were recommended to change SOLI to Austria but it was voluntary the company didnt mandate it. For UK based crews an EASA license meant when required /on occasion they could be positioned out to Europe to do flights for the EU/Austrian AOC. Many saw this actually as a disadvantage, when you live near Luton or Gatwick who wants the inconvenience of getting positioned out for the occasional flight or two.
As said 60 percent of the Easy fleet is G Reg, from 2022 EASA validations on the G reg expire hence all will require UK FCL. All the UK based Easypilots that SOLi to Austria will now I expect be applying for UK FCL on the 1st April.