I say it will be Turkey, in alliance with China as they rebuild the Ottoman Empire. A declining Russia is a pre-requisite, and this Ukraine gambit, may be the beginning of the end for a strong Russia and the beginning of the rise of Turkey.
Erogan has indicated in the past he would like close (perhaps very close!)ties with Turk ancestral homeland - Turkmenistan. A lot of that real estate in between maybe could be persuaded to cooperate.