Ethnic cleansing and settler colonialism on that scale might sadly work somewhere more thinly-populated, like Siberia, but the scale of the Central Asian steppe would make it impossible, particularly given that a lot of the native populations on the steppe are already entrenched. The Karluks of Transoxiana, for instance, converted to Islam six or seven centuries before the POD and hung on to have their language become the main trade language within the Chagatai Khaganate; we still have Karluk-descended people hanging around today in the form of 30 million Uzbeks. We still have several million of the Persianized and Muslim descendants of Oghuz Turks hanging around on the steppe. Even among the Kazakhs, you've got 15 million of them today, plus Islam already taking root there from the 14th century. Add four million Kyrgyz plus Cumans and Mongols and a bunch of other Turco-Mongolic groups, and that grows substantially. Even accounting for 16th-century populations, that is a lot of atrocities for Russia to commit, over an enormous and challenging geographical area. It would probably end up being far and away the single largest deliberate genocide in history.
I'm not sure that level of deliberate atrocity is even possible, and I wouldn't want to write that timeline. It makes me sick just thinking about it.