Uhm, no, the Siri Theory is not the least bit far-fetched. There's a significant amount of evidence for it. One of the most succinct and yet comprehensive that I've seen is here:
https://tinyurl.com/2p9rfpc5This doesn't consist of merely fantasizing about the smoke signals coming from within the conclave, although those help corroborate the abundance of other evidence in favor of the Theory.
There are a number of independent sources, and one of them, Scortesco, a counsin of the Vatican Noble Guard, who were responsible for guarding the conclaves, was burned alive in his bed shortly after he published his letter with the details.
Paul Williams, former FBI, wrote a book where he mentioned in passing, in a footnote, that Siri had been elected and had taken the name Gregory XVII, citing classified docuмents. Williams is not a Catholic and didn't consider this particularly important. While the docuмent has never been found, presumably RE-classified after the book, it's unlikely that Williams just made this up. He gives the exact name and date of the docuмent and mentions a detail about the papal name, Gregory XVII ... that a non-Catholic wouldn't even understand the significance of, i.e. that it means he had accepted the election, and for him to land on "Gregory" as a non-Catholic was also unlikely. We can hardly doubt that both the US and USSR had agents in the conclave reporting back to them.
And it's the perfect plan, if you think about it. Let Siri be elected (his election was considered a foregone conclusion, as he was considered THE papabile for that election), then force him out uncanonically, so that their agent would not legitimately hold office, and therefore would not be protected by the Holy Spirit. These enemies of the Church had more "faith" in the protection of the Holy Spirit over the papacy than R&R do. They knew that if Roncalli had been legitimately elected, that God would cause him to drop dead before he and his successors could damage the Church as much as they wanted to. I look at this as the "uncanonically-elected pope" reference in the prophecy of St. Francis of Assisi, not Bergoglio. Bergoglio was just the last in a line of illegitimate usurper Antipopes, who were not merely otherwise-sincere people with confused minds who got elected due to the overall liberalization of the Church ... as the R&R narrative holds. Regardless of how "confused" they were, the Promises of Our Lord for the assistance of the Holy Spirit for the papacy (something +Lefebvre ackowledged) would absolutely have prevented a legitimate "confused" pope from wrecking the Church.
But I urge people to look the link above. There's a ton of evidence all pointing to the same conclusion.
As for the Bennyvacantist equivalent, while the non-resignation theory is absurd, the St. Gallen mafia collusion has actually been admitted by one of the participants, and that's actually a legitimate reason for Bergoglio to have been disqualified, as JP2 explicitly stated that collusion over the election would render it illegitimate in his docuмent about the conclave that would occur after his death. Where the Bennyvacantists miss the mark is in believing that the Crisis in the Church started with Bergoglio and in thinking that we don't have a bigger problem here that goes all the way back to Vatican II. Bergoglio was simply the most brazen about it, but the heresies of Wojtyla and Ratzinger make his absolutely pale by comparison.
And to top it all off, this happened shortly before the conclave:

This White Dove / Pigeon landed on Cardinal Siri's head as he offered Mass. He reportedly continued with Mass while ignoring it. White Doves are universally acknowledged to be the symbol of the Holy Spirit, and this incident was taken to suggest that the Holy Spirit would choose him to be the next pope. Perhaps a coincidence, but I don't think so.
This is from the accompanying newspaper article:
“Pigeon perches on Cardinal’s Cap – Genoa, Italy – Giuseppe Cardinal Siri, Archbishop of Genoa, remained unperturbed when a pigeon perched on his cap as he celebrated Mass in the arena of the Orfei Circus here. The pigeon was one of a flock released in tribute to the Cardinal. The Mass, said on an altar set up in the center ring of the Big Top, was attended by circus entertainers and a crowd of Genoese.”