Sorry Genghis, EASA is not becoming a full ICAO member. The EC Commission would like the EC to become a member instead of the individual member states but that would require a renegotiation of the Chicago Convention which is unlikely.
It is also incorrect to say that EASA has got every right to insist upon any aircraft based within an EASA member state being registered there. As I understand it the EASA regulation does not give it the power to do this and the EASA consultation is in connection with advice that it has give to the Commission about the extension of the Regulation to cover operational and licensing rules. To introduce such a requirement will require a further Regulation which must be approved by both the European Parliament and the Council.
However, I agree that the EC has every right to pass such legislation and I do not see that it will contravene member states obligations under the Convention.