I donīt see a problem with easyJet asking pilots to change their licences to UK state of issue.
As others have mentioned earlier, this has been the norm for years at easy. And they have paid for the conversion as well.
When I joined they said that f.ex. the Belgian CAA would not accept a UK examiner signing the licence.
Another example is Sterling Airlines in Denmark, they require all pilots to have a Danish JAR licence, who in my experience are a lot more difficult to deal with than the UK CAA.
Furthermore, in Denmark the yearly fee (yes you normally pay for a yearly renewal, not like a 5 year renewal in the UK) is almost identical to what you pay for 5 years in the UK. (Makes economical sense to have the UK licence, no)
My two cents worth,