If we hear Palpatine talking to Kylo from day one, that kinda renders the reveal that he’s been every voice meaningless because he’d already a prime suspect out in the open. For it to really be a twist that catches Kylo off guard it would make more sense for him to hear solely Vader’s voice, which would make more sense given the context of him communing with Vader’s spirit through his melted helmet. There could be an instance or two of Snoke’s voice in Kylo’s head, like maybe when he’s about to kill Leia. Then when Palps say the line, it’s like “Oh wow, Vader’s ghost, and those telepathic Snoke messages, those were Palpatine all along?” It would really shake up the audience’s and more importantly Kylo’s perspective. The scene of Kylo communing with Vader’s mask in TRoS could be pushed up to TLJ to build up this aspect before the Palpatine reveal, so we see it as something he does regularly before its true nature is revealed.