Alternatively, the Orthodox could be polite and allow Catholics to attend, as the Catholic Church has allowed Orthodox to attend councils...Or even better, the Orthodox could join the Uniate Churches in rejoining the Universal Church (however you want to cut it, either a gradual drift or an Orthodox departure, the Catholic Church was never a part of the Orthodox Church, and thus never "left Orthodoxy").
(...the Catholic Church was never a part of the Orthodox Church, and thus never “left Orthodoxy”)
That depends on which version of history one is reading. Rome claims all of the other patriarchates left the Catholic Church. Our view is that Rome left the Church through her insensate, and often self serving, doctrinal innovations.
“Alternatively, the Orthodox could be polite and allow Catholics to attend, as the Catholic Church has allowed Orthodox to attend councils...”
Don’t hold your breath waiting for any generosity from the Eastern Orthodox. We can give them a free church they have no claim to (https://news.google.com/newspapers?nid=1876&dat=20030525&id=Y4IgAAAAIBAJ&sjid=UNAEAAAAIBAJ&pg=1864,5713648&hl=en ) while they cannot muster up the guts to give our own churches back to us without public shaming: http://articles.latimes.com/1990-03-17/entertainment/ca-317_1_orthodox-church
I hope the pan-Orthodox council does some good. It would be great if they could solve some of their ridiculous problems (and we have plenty of our own), but I until I see it, I will have to assume little will be done about the HUGE issues like the schism in Ukraine. Without a pope, ain’t much gonna’ get done there about that!