It seems to me that the Filioque is almost a non-issue today. People understand that *in the Creed* it's a mistake and also the broader Orthodox sense of the expression in which it is correct.
Do you what would cut the union as correct and acceptable to me? A "new" Creed detailing those ambiguities.
Specifically, something more or less like this:
"We believe in one triune God, one unknowable essence, Three Persons, many energies; We believe the Father Almighty, Maker of heaven and earth, and of all things visible and invisible..."
"... and was incarnate of the Holy Spirit and the Virgin Mary, and was made man, uniting in His Person human and Divine natures, wills and energies."
"... who proceeds from the Father and is sent to the world through the Son, the only Infallible and Inerrant Teacher of the Church, who blows wherever it wills..."
"...and in the Church, One, Holy Catholic, Apostolic, Orthodox, Visible, Undivided, Mother of the Scriptures, built on the Son, its only Rock and Head, earthly governed by the Bishops, who all sit on the Throne of Peter and are equal in honor, dignity and whose orthodoxy of faith create their authority, first among them, the first in the Diptychs in honour of orthodoxy of faith and tradition".
"We acknowledge one Baptism for the remission of sins, and one chrismation for the seal of the gift of the Holy Spirit. We believe in the real Presence in the Eucharist, and that the bread truly becomes the Son's own most pure Body, and that the wine truly becomes His own most precious Blood."
If we all could agree to this Creed "who's guilty of what in the past" could be relegated to a discussion of history only, and, I belive, union would be true and complete.