If this new rumor comes to see the day of light, then we could see Brock Rumlow aka Crossbones return to the MCU once again. According to a new report from MCU Cosmic, Marvel is currently looking for a way to bring the character back into the fold. The last time we saw Crossbones was in Captain America: Civil War where he meets his demise via suicide bomb/Scarlet Witch in an attempt to kill Captain America.
We then see Brock Rumlow as a S.H.I.E.L.D./Hydra Agent in Avengers: Endgame when The Avengers travel back in time to the events of The Avengers (2012). According to a previous report from MCU Cosmic, Doctor Strange in the Multiverse of Madness will be featuring known MCU characters from alternate realities. Coinciding with this new report, Crossbones could be one of those characters. Additionally, all depending on what capacity Crossbones is brought back, he could be a mainstay in the MCU to be an adversary to Sam Wilson and/or becoming a member of the Thunderbolts.
Source: MCU Cosmic