There is nothing to expand. The Creed deals with the origins of the Holy Trinity. There is also nothing to stop the Church from teaching those who are not undergoing catechisis the difference between the origin of divinity (the monarchy of the Father) and the Divine Economy of our salvation, in which the Holy Ghost is sent by the Father through the Son.
Catechism and Creed are two different things. You can expand all you want as an expansion, but not change the Creed.
This presumes that there is no authority at all besides an ecumenical council; in one swoop, you invalidate not only the papacy, but also the Roman patriarchy
It does not invalidate the papacy. It is latter-day Roman Catholicism that completely invalidates the council authority. In the Undivided Church of the first millennium, the pope was an integral part of the councils but not the sole or even the final authority. The 'authority" of the pope to proclaim dogma without a council is a Vatican I aberration.
I disagree with the Orthodox concern that somehow the Filioque Creed risks doctrinal confusion, because, as I wrote K, the creed plainly states that the Son is begotten of the Father.
Well, apparently it does.
That's good news.
Gotta run.