Certain areas are quite dangerous for Russia to mess with because they are areas of Japanese interest, including southern and central Manchuria and eastern Inner Mongolia. Russia would only go after these areas if it has chosen a path of revanchist confrontation against Japan for the "Rasplata' the 'payback' and abandoned its policy since 1907, and strengthened after 1911 of recognizing separate spheres of interest.
If it stays off Japanese turf, this leaves pretty much northwestern regions like Xinjiang, western Inner Mongolia, and possibly Gansu province or parts of it for Russia to puppetize. Aggressive puppetization in Xinjiang could start to rub Britain the wrong way.
One thing to note though is that without WWI, warlordism might not deteriorate as badly, because the debate over what stance to take on the war was one of the significantly divisive issues for the Beiyang Republic government and army.