As with all conspiracy theories, to render them plausible you have to provide a reasonable cui bono?.
I have yet to see anything that +Vigano has done that benefits the conspirators. If he were an agent of controlled opposition, he'd be herding people back into the Conciliar Church, Motu and FSSP style, but instead he's swung clearly to the RIGHT of the FSSP and SSPX on several issues. He's standing a hair's breadth away from sedevacantism, and currently seems to be of a Resistance mindset. He's even made a reference to the Jews being involved in the attack on the Church.
So this conspiracy theory I consider to be total bunk.