I forgot the important part: The electrical system. To the best of my knowledge all of the new countries use 230/400V @ 50Hz. (Cyprus could still be on 240V, they didn't reply)
Two of the countries use the British 13A plug: Cyprus and Malta. (Although the plug(s) used in the Turkish community on Cyprus is an open question)
Estonia and Latvia probably use the Schuko. (Strong Swedish and Finnish influence in Estonia) Lithuania uses the Shucko or the French socket. Poland the French (this is the Gost standard), ditto for Czechia and Slovakia. Hungary and Slovenia both use the Schuko.
Possible future members Norway, Iceland, Romania, Bulgaria and Turkey all seem to have adopted the the Schuko as standard.
It would thus seem that a common European plug is becoming less and less likely. It would have been easier twentyfive years ago when every member state had its own plug.
