Well what you have said here is true..But you have to consider the balance of power in the region..Regarding Russia, you need to pay extra attention to Putin`s political rhetoric about Armenia, Georgia, Southern Caucasus, Syria etc. For all of those, Turkey`s and Russia`s national interests contravene..As of now, SCO might not be a military alliance, but imho it surely will morph into one soon, global balance of power dictates so..All in all, there shouldnt be any "strategical"( or lets say big, important) conflict of interest between Russia and Turkey for them to be in the same pact/alliance...You can ask "then how in the world Greece and Turkey are both Nato members?" It was because of USSR threat
Thats why i said unrealistic..I dont know about China but imho Russia would never allow Turkey to join SCO because we are simply regional rivals