I don't think that Medvedev will be the next president of Russia. He is too weak and pacifist. Putin might prefer someone who is a bit more aggressive, perhaps Ramzan Kadyrov or Sergei Shoygu. But the issue here is that both of them are not ethnic Russian and Orthodox Christian. The former is a Chechen and Muslim, while the latter is ethnic Tuvan and Buddhist. Putin himself is part-Karelian and Vepsian, but at least he is a Christian, so his ethnic background is not much of an issue. So the choice narrows down to Igor Shuvalov, Dmitry Kozak, Dmitry Rogozin, and Alexander Novak.