But you suggested it....sedevacantists
This would mean that not only is Francis not valid, neither were Benedict, John Paul I & II, Paul VI and John XXIII. I reject this position because I think it contradicts Matthew 16:18 and 28:20. Even with the Western Schism and Avignon Papacy, the Church was able to go back and determine which pope was valid, we don't have that here.
The ONLY reason I could think of to invalidate Francis is if it was revealed that Benedict was forced to step down and there has never even been a hint of that.