I don't see why that should make any difference. The Senate was there using the same constitutional advice-and-consent power that is at work in the Estrada matter. If it's legally wrong to filibuster Estrada's appointment as circuit court judge, I do not see why the filibuster of Fortas's elevation was not equally illegal.
Conversely, someone not on the court being blocked for appointment to a court, and someone on a court being refused leadership of the court but still staying on the court.
-PJ