Mike has mentioned it himself, actually. He's been impressed with Akesson's work, but he has told him to redo some of his solos. I think it's good for Fredrik to have someone who will push him to do things differently. Mike knows what he wants, and I think that as Black Session said, his skills will just be another tool for Mike. And, come on....Fredrik knew what he was getting into. I don't think expects or wants Opeth to be a shredfest.
But more to BS's original post, I don't think that the dynamic set forth by Mike and Peter will really change with Akesson's addition. Mike enjoys soloing too much, don't you think? There haven't been lead guitarists in Opeth before, and I don't anticipate there will be in the future, regardless of what sort of label Fredrik comes in with.