I doubt that there will be any thrust from Sumy in the direction of Chernihiv. The Russians have learned the very hard way not to rush vehicles and infantry ahead of supplies and without adequate air support in heavily forested territory where they do not already have significant material and human infrastructure support (unlike in Donbass). If there is to be any attack on Chernihiv City it will come from the Bryansk Oblast or Belarus.
It doesn't have to be that kind of thrust though does it?
A slow and careful incursion into the Northern Border at this time could be the kind of distraction that the Russians need to be able to keep the final momentum going in the Donbass.
Its a form of throwing in the reserves as soon as the enemy defenses start to crack and collapse. In this case it would be not so much putting more troops into the existing Donbass salient (as I am sure they already have all they need to do the job) but to divide and draw off the reserves from the Ukrainian army that would otherwise continue to reinforce the troops in the Donbass.
I believe we are already seeing such a move around Karkhov, so a a further move around Sumy could be the straw that breaks the camels back. I am thinking specifically about the further complications to the Ukraine's supply logistics, which complaints from their front, rather suggest are already a mess.
