No one has the authority of course to bind consciences with such a declaration, but I am a firm believer that if someone of +Vigano's stature started the ball rolling, any Catholic who still has faith left will come to agree after some time has passed. Then if there's a Universal Consensus that the See is vacant, there could then be an election. Problem with the Conclavism of the past that brought us the likes of Pope Michael and Pius XIII and Linus II is that such a thing requires a near-universal consensus. It has to be an act of the entire Church, not David Bawden's mom and ex-girlfriend. As it is, most Catholics recognize that Bergoglio is not a Catholic pope and not their rule of faith ... but just differ regarding the legalities. Heck, many of the Modernists who were excommunicated by St. Pius X would themselves excommunicate Bergoglio for heresy.
Declare the seat vacant? Cardinals cannot declare the seat vacant - just remember that the cardinals served their purpose when they elected him. Nor is there even a need to start that ball rolling - by him or by anyone.
What he can, should and is supposed to do is what God expects him to do....
"However, even though the hierarchy cannot take legal action against an heretical pope, all of them together,
or any one of them in particular, can condemn his teaching; they can accuse him before God's tribunal, warn him of his sins, and remind him of the divine wrath.
Should this measure fail to produce any correction, they can
denounce him before his subjects, the Catholic faithful, and warn them that they are not to listen to his teaching. Indeed, not only may the prelates of the Church do this, they have a most serious obligation to do it, an obligation which is as grave as the heresies are pernicious and scandalous. And if they fail to do this, they become a party to the pope's crimes, and will most certainly share in his punishment..." - Fr. Wathen's book, Who Shall Ascend?
This has the chance of bearing good fruit, whereas attempting to "get the ball rolling" achieves nothing good.