This is interesting : you're saying effectively that another European country could authorise the use of an FAA/PPL/IR in all CAS in aeroplanes of their own national reg ?
Yes.
But, as always, there is a catch
JAA bans its member states from validating ICAO (non-JAA) IRs beyond one year. I have the URL to the JAA document somewhere and will dig it out if you really want it.
So, the CAA's continuous validation is a pretty good deal - even if it is all but useless due to the "OCAS" requirement.
So, JAA have put the boot in, to make sure that none of the new JAA members do what would be a really obvious business opportunity
The "bizjet registry countries" e.g. Caymans, and now the IOM, fully accept FAA licensing and certification, but this is not useful to our sort of GA because they impose minimum weight limits e.g. 5700kg.