Sure. The Pope can say that from now own the Catholic Church is erasing everything that was passed after the Great Schism and we are starting from ground zero, with all theological innovations on the table for a discussion. Done.
That won't happen, however. The other more realistic, possibility is that an Orthodox-Catholic body works out theological issues without a council and puts them to each Church's decision-making body for acceptance, i.e. to the College of Cardinals with the Pope presiding, or the All-Orthodox Council (Synod) of Bishops, with the Ecumenical Patriarch presiding in Pope's stead, according to the ranking order established by the Ecumenical Councils.
In the west, a stamp of approval would be made part of the obligatory acceptance. In the east, the acceptance of the clergy would have to be verified by the laity and lower clergy. This is what happend in Florens (13th century) when the False Union was agreed upon for political reasons, and rejected by the non-cerrical member sof the Church. This approach is posisble but very unlikely.
The most realistic option is for the East and West Churches to agree on the scope of Papal jurisdiction, which is an issue of serious proportions. The East makntained, and is backed by Ecumenial Councils, that the ope does not have authority in other patriarchates but his own, even though he is a the first among equal among Patriarchs. Inf this is possible, then the Pope would convene a General Council to work on theological issues. This approach is possible and somewhat more likely, but ti will happen at about the speed of a glacier.
What I don't understand is how an Ecumenical Council can be an Ecumenical Coucil when all the bishops are not in communion.
Well, the Ecumenical Councils were called when certain bishops were excommunicated or about to be excommunicated for teaching false doctrines (doctrines not known to the Church, or doctrines contrary to the Holy Tradition of the Church -- which is to say, the Scriptures, the Apostolic teachings and the previous Councils).
The veracity of Orthodox teaching is estabished by going back and checking how much we have straiyed from the earliest recorded positions on the subject of the Apostles and Curch Fathers.
That sounds like the most realistic option to me as well.