As I understand it many Chalcedonian and non-Chalcedonian Orthodox are coming to the conclusion that the differences leading to separation were more terminology than substance and that they don't really disagree.
True. Both the Syrians and the Greeks have held no Ecuмenical Council of their own since they separated from Rome long ago, the schism of the one lasting over 1500 years and dating from the Fourth, that of the other close to a 1000 years and upto the Seventh. It is a curious fact, but both appear to concede tacitly, then, that the Bishop of Rome's consent at least is necessary for a Council to be Ecuмenical.
So far as the Catholic Church is concerned, the dogmas established in Chalcedon are not negotiable. It is no more permitted to claim there is only one nature in Christ than it is to claim there is only one person in the Holy Trinity. For since it is clear that Our Lord took to Himself and retained a true human nature, along with its integral faculties such as intellect and will (as is plain in the Gospel and Our Lord's prayer in Gethsemane) into His Person in a Hypostatic union, the distinction must be necessarily made, without the division of His person nor the fusion of the natures, the terms used properly and consistently, and the doctrine formulated with precision.
Now, the Church has always been ready and willing to explain and defend her doctrines and to make it easy for those unhappily separated from her in times past to be quickly reconciled, as she did in both Lyons II and Florence. So by all means, let the Church work toward that, but make sure and see to it that they genuinely come to a true and orthodox understanding of the Incarnation and of Christology. There is a minimalist tendency today to pretend that dogma and doctrine and its exact formulation don't really matter anymore which must be avoided here.