It has been suggested that the prime motivator for EASA is Aerospatiale. If you look at the EU documentation it is all about getting europe-wide certification for commercial air transport.
I believe that we are likely to see ICAO licenses and ratings accepted across the EASA states. i.e. if you have an ICAO license or rating issued by one EASA state it will be valid in any other EASA state. So you could on the basis of a UK PPL fly a French Registered aircraft in German airspace for example. Commercial pilots would be able to move between EASA carriers without problems.
Purely UK licenses and ratings which do not have an ICAO equivalent such as the NPPL and IMC look unlikely to be extended europe-wide.
EASA have already recognised the impracticality of some of their proposals and gliders and permit aircraft are continuing for the time being to have their airworthiness ensured by national bodies rather than EASA.
The PFA have some explanatory info
here
Mike