I am not sure SV is doctrinal.
Coming to the SV conclusion is indeed applying what has been taught by the Church in times past but the Church has not taught on the subject today, because it can't, there is no Pope to do so.
SV is a practical application of Church teachings but I do not believe that one who does not accept this is a heretic (formal or material). He simply does not know.
It will take until we get a valid Pope to settle the question which will then be mute.
But again if a legitimate Pope can do, say and teach with the conciliar "Popes" have done and be valid then there is no reason to have a Pope.
The legitimate reason for a Pope is to have a unifying head, these guys divide by contracting in their words, writings and actions the perrenial teachings of the Church over and over again. If a legitimate Pope can do these things there is no reason to have a Pope.
Anyone get my drift?
He also is to have the final say. But he doesn't. The SSPX tells us whether he is right or not. Such would not be necessary where there a Catholic (the only possible kind) Pope ruling God's Church right now.
Get it? I hope so. I'm not sure how it can be more clear for those with eyes to see.