The Russians make the largest production helicopter in the world, the Mi-26 “Halo”, and they have been considering an updated helo in the same (humongous) size range for some time.

Now, it appears that they are looking to do a joint venture with the Chinese to develope a 20T payload class helicopter. (paid subscription required)

Seeing as how the helicopter originally flew in 1977, and has been in service since 1983, there is a lot of room for improvement.

Just updating the transmission to modern aluminum alloys in the transmission and going with a more modern rotor system would probably add about 10% to payload and range performance, but that would be an upgrade rather than a completely new design.

A completely new variant might be based on the canceled Mi-46, though that was about a 12 tonne class machine.

I think that the reason for a joint venture has more to do with a potential market, they want to sell to the Chinese, than it does to any real technical or development advantage that they might gain.