If ADU stands for any one thing within theology and ecclesiology, it is for re-union of Christian churches, the one church of Christ invisible made visible on earth, as God's will is done in heaven so it should be on earth. Starting with Anglicans would be a fine thing :)
Thus music to my ears is this report on a recent Orthodox-Catholic agreement.
Noteworthy in this report here is a more careful approach to actual history of East-West relationships, setting aside as much ecclesial prejudice and scholarly bias as possible, with the upshot that, hey presto, the truth wins and paves the way for the light of rapprochement to be seen at the end of the tunnel of separation. It is still a long tunnel but maybe, just maybe, a pinpoint of light at the end is in sight!
Oh, happy day ...
See also now a Russian report on the same meeting, which draws our attention to the somewhat deferred question of Uniatism.