Seems to me it'll take someone younger, with size enough to reach Wlad Klitschko's chin and power enough to hurt him when he does get through. Another Lennox Lewis.
This whole situation is bizarre. It's like you've got one heavyweight champion with split personalities. The two-headed Klitschko will never fight itself. Their promoter will hand-pick opponents best suited to each brother's particular skill set. This cries out for a single World Commission of Boxing. But then you'd likely have one brother acting as gatekeeper for the one with the title, so you'd still probably have to beat both of them to be champ. However, if they refused to match them against each other, there'd be pressure to allow a top contender to bypass the gatekeeper.
Sooner or later one or both of the brothers will retire.
Well, at least the boxing world makes sense in Title Bout....unless you're a masochist.
Cap