SSPX: Formal schism or informal separation?

For those interested in the relations between the Society of St. Pius X (SSPX) established by Msgr. Lefebvre and the Holy See, particularly as regards the quest to fully re-unite them to the Church, there is an interview with Cardinal Castrillon Hoyos (pictured here celebrating a Solemn High Mass in the classical rite at St. Mary Major) in 30 Days here:

Interview with Cardinal Darío Castrillón Hoyos, President of Ecclesia Dei, on relations between Rome and the Lefebvrians

Brian Mershon has added his voice to this question over at the Wanderer in this article:

The Society of St. Pius X and Vatican II