yea thats why i was proposing the 250 dual as it can run on diesel on that section of the line without needing a drag or loco swapNo the trans-mongolian is not electrified. Not that it should be difficult, though : I don't remember having seen any tunnel on that route, and bridges are not very frequent either. Supplying electricity might be complicated, but with a 2x25 kV scheme, you don't need that much injection points. Traction becomes diesel as of Ulan-Ude in Russia, till somewhere in China ; when I did the trip, a chinese diesel loc took us all the way from the chinese border to Beijing.
dont think any part of the line even reaches 250 past china so no real need for a 300/400km/h EMU