On a more serious note I hope the recent talk about increasing our nuclear arsenal isn't in response to background information about stuff like this with the intention of keeping pending likely conflict remote and conventional.
Russia doesn't need to move S-400 forward their existing installations are within range for general purposes additionally can be complimented by more mobile assets for point defence, etc.
Russia has only moved around 1/10th of the assets up though compared to what they'd need for a larger scale incursion never mind full scale invasion but coming up to the time of year where conditions are more favourable for heavy armour movement and a longer campaign so always a bit concerning. If something bigger scale does happen probably more towards May with less risk of weather bogging things down.
I'll admit I've not looked into where their s400 units are placed in that region.
How much in the way of heavy armour arty do the ' separatists ' have in the region.
I've read that crimea is having a major drought due to a major canal from the Ukrainian mainland side being cut off, possibly could be planning an incursion to secure this?