There's a simple reason why the Mormon Church (Utah offshoot) will never, ever admit that Brigham Young was in the wrong, about anything, ever.
If they admit that Young introduced and practiced the evil blood atonement doctrine (and that people were subjected to what amounted to ritualistic killing for "crimes" like having a Mormon leader covert your wife and or goods) and admitted that Young ordered and covered up the Mountain Meadows Massacre, and that he made millions of Dollars by ripping off the handcart pioneers, and that he ordered and covered up the murder of dozens of outsiders in case they might be government spies and that he almost certainly 'stole' the presidency of the Mormon Church, tThey would then have to admit that Young was not only a "fallen prophet" but that he stole the leadership by subterfuge and criminal acts.
So, therefore in admitting that Brigham Young was not the rightful successor to Joseph Smith, they would have to acknowledge that the RLDS (or one of the other offshoots) was the rightful successor to Joseph Smith.
That will not happen anytime soon. Although I suppose there is a Small chance that such a rapprochement might occur some time within the next 50 years, though this does very muh depend on how the Utah Mormon leaders react and if they can take the majority of the people with them. Some diehard Utah Mormons wold probably seek out the polygamous sects to join.