England is a bit different in the sense that there still is a sense of meritocracy - players are confident enough to become specialists, knowing that their place in the white ball team is safe, so long as they are good enough.
With Pakistan, I don't think that is the case - there is still a sense of insecurity regarding places and selection. Usually, we see players hang on to any position they have in order to prolong their careers, and earn any available income that comes their way. That way, it would be difficult to see someone voluntarily forgo a test team place, at the risk of someone else coming in and establishing their place and name, who could eventually challenge them for a white ball team place. And, as others have mentioned, its not like we really play enough test cricket for fatigue to become a serious enough issue that players are forced to pick to do down one route only to prolong their careers.
It would have to be a well established player, like an Afridi, who feels that their position is secure who takes the risk. At the moment, I am not sure there is anyone who fits that mould.
