The CAA have already said that there will be a direct CAA PPL to EASA PPL transition:
Aeroplane and helicopter licences (and associated ratings) that are issued under national requirements (not JAR-FCL) and are compliant with ICAO Annex 1 will be converted to EASA licences in accordance with the second annex to the Part FCL regulation. This will apply to UK national aeroplane licences other than the NPPL(A), and to all UK national helicopter licences.
From
this document.