This is a very different issue, as you well know. The Eastern Orthodox churches, while not in communion with Rome, have validly ordained clergy and recognize the Real Presence. Quite different from concelebrating a mass with a protestant minister.
We will celebrate this Great Jubilee on our pilgrimage towards full unity and towards that blessed day, which we pray is not far off, when we will be able to share the same bread and the same cup, in the one Eucharist of the Lord. (John Paul II & Patriarch Bartholomew, Common Declaration 29 June 1995)