Despite Wayne Allwine being the official Mickey Mouse voice since the late 70s, there have been others - and still continue to be others - voicing the character at times. Since his death, his understudy, Bret Iwan, is the official voice actor for Mickey, but again, there are occasionally others, such as Chris Diamantopoulos for those animated YouTube shorts - mainly because since those are modeled after the classic Disney shorts of Walt's era, they wanted somebody who sounded more like Walt's Mickey Mouse voice . . . so, depending on what, exactly, Disney wants, my guess is they'll bring in anybody who they feel can give them the particular sound they want for Minnie in whatever project they're working on. They've already got Tress MacNeil, who is easily one of the voice acting queens of our generations, doing Daisy . . . if she can reach a register much higher than Dot/Babs/Gadget, they may even use her for Minnie.