It wasn't much a vague hypothesis but things that were on the process to happen.
Black Isle, the devellopers of Fo2 were going to make Fallout 3 - Van Buren, while the new leadership of Interplay (after Brian Fargo left) shutted down the project at mid-develloppement to make a console POS.
When that new interplay decided to sell the IP, Bioware & Troïka tried to buy the IP, but were outbidden by Bethesda.
Troïka was made by the three main creators of the Fallout IP, and were devellopping a post-apocalyptic RPG without a name during that period. It is likely that it would have been the next Fallout, had they won the bid. A Fallout made by its creators would have very low chances of failure.
While Bioware lack some writting skills, they have some experience with RPG and are friend with Obsidian/Black Isles. They could have made an average/good rpg or called Obsidian for advives, or outright develloppement, as they pretty much asked for them to make a few of their own sequels. (not sure what would have happened after EA bought them)
So at least 3 Fallout sequel that were very possible at some point.
It just happened that Bethesda/Zenimax threw more money on the bid.
Although, other likely hypothesis would have been that Fargo would have not burned out and kept control of Interplay (he had refund 90% of his debt when he gave up to the investors pressure) OR that the new leadership of Interplay would have buried the IP instead of selling it, so another creator would have bought it at low price a few decades later to kickstarter the sequel.
Although, a Fallout sequel too early could have lessened the success of the Wasteland 2 kickstarter. The guy litterally made millions on the disapointement of Fallout 3. If Fallout 3 wasn't so shitty, Wasteland 2 kickstarter wouldn't have so much success and wouldn't have brought so much coverage to the kickstarter system. A coverage that benefitted other projets like Pillars, Torment etc...
I cross the fingers that they will be 1-2 good/average Fallout in the future (no matter how much time we have to wait), but i am totally into all those new good games that were made possible and more successfull because of Fallout 3 failure. Also, let's not forget that FoNV come from the same publisher than Fo3, so even that publisher can be redeemed sometime.