Did Rome ever really give any indication that they'd accept anything less or was the idea that the Pope was pleased with the Preamble as adjusted by +Fellay merely a rumor?
There was clearly a deal in the works, but one side or the other got cold feet.
I'm guessing that when they realized 3 bishops might split off it would destroy the legitimacy of any sort of canonical recognition.
The practical implications of a canonical deal though are staggering when you think about them.
Consider the fact the SSPX would have to recognize conciliar annulments.
(I wouldn't be surprised if there would be certain people, perhaps wealthy eople, who would be supporting a deal for that reason.)
You can be sure the SSPX processes would be liberalized, if they were even allowed to keep them.
Really you can't have two religions in one structure, that's why a deal will mean the end of serious traditionalism in the SSPX.