Estonia, Latvia, and Lithuania are also putting in a "standard gauge" line, so they can interoperate with the rest of Europe.
What coupler are they going to use? Switching from Russian automatic couplers to European buffer and chain freight couplers is a step backwards. (It's amazing that the EU hasn't modernized freight couplers. There was something called "Eurocoupler" proposed in the 1970s, but it was never implemented. A "Digital Automatic Coupler" with data passthrough is being proposed now.)