Addition by subtraction: by shifting the border between Ukraine and Russia a bit to the west, the percentage of people within Ukraine who are Russian-speaking falls. The remaining Russian-speakers won’t be so large a minority as to divide the political spectrum in Ukraine along Ukrainian-speakers and Russian-speakers. This change in the electorate will secure the slightly-shifted border.
Having said this, I will now say what is the danger of this: To a junkyard dog like Putin, compromise is seen as a sign of weakness and an opportunity to again go on the offensive. It is one thing to say that changing the electorate will secure the border. That’s only partly it. You also need a wall backed by a border patrol and, if necessary, the military.
Ukrainian joke: In Ukraine, an optimist learns English, a pessimist learns Russian, and a realist cleans his gun.
When Poroshenko took office, the first thing he did was say no Russian was to be spoken in Ukraine. That was changed shortly thereafter.
Russia wants to include Ukraine as US wants to include Mexico. Doesn’t worth the trouble.