I read some where that Russia is getting ready to deploy S-500 systems FWIW.
I have read the same thing.
I believe the S-500s will be deployed in the Moscow region and the S-400s from Moscow will then be forward deployed to Ukraine.
My guess is ruzzia will not forward deploy the S-500s as they cannot afford to have them defeated by ATACMs.
This is the same rationale that ruzzia is not using the Su-57s in Ukraine for fear they will be shot down by Patriots.