I'm curious to see +Vigano's reaction to this excommunication.  Will he ignore it, or will he act as if its valid?

Yes, that would be interesting.  However, two thoughts:

(1) This was written almost 2 months ago.

(2) It's Ron Conte. 

Does Vigano even know of him/know about the "excommunication"?  If he does, would/does he even care what he thinks?

Maybe he would if his purpose is to convert the Novus Ordos.

The idea that an evil intention deprives someone of office is the very foundation of the Cassiciacuм Thesis, and yet I don't think I've ever seen them quote one canonist or theologian who ever said this.

  No, it's not.  It's peripheral.  It's merely one explanation for WHY Bergoglio et al. didn't have formal authority.  Another would simply be manifest heresy making them non-members of the Church.  I've explained this several times, but this falsehood keeps resurfacing.

What's at the core of the Thesis is the distinction between the legal appointment to office and the ability to formally exercise the authority of the office.

St. Robert Bellarmine cited Pope St. Celestine's declaration regarding Nestorius, that Nestorius lost his authority from the moment he began to "preach" his heresy (i.e. became a pertinacious manifest heretic) while not being formally removed from office until a couple years later.  He said that during the interim period (between his manifest heresy and his legal removal from office), Nestorius was in a state of excommunicandus, not unlike the state of "suspension" in Father Chazal's variant of sedeprivationism.  This is where the Thesis finds the right balance between the Church's authority and the incapacity of an individual to exercise the office.  This incapacity could be caused a number of factors, and the defect of intention is one speculative explanation for it, and is not "the very foundation of the Cassiciacuм Thesis", as has been falsely claimed.  So, for instance, a layman who's elected pope but isn't consecrated a bishop becomes the Pope immediately upon acceptance, and can probably exercise certain administrative functions of the office, but cannot, for instance, teach the Church.  Other things that might exclude from formal exercise of office are manifest heresy and defect of intention.

In terms of a "Canonist" or "theologian," who's said this, it's universally held that the elected, the candidate, must ACCEPT the office in order to become the Pope.  Pius XII even mentioned acceptance in his docuмent on the then-future papal conclave.  So the argument here is that Bergoglio et al. did not in fact accept the office of the papacy for what it was intended to do.  I don't find this the most convincing reason, and it's held by Bishop Sanborn and some of the Italians, but, to repeat, this is NOT central to the Thesis, much less is it "the very foundation" of it, as you claim.