I will be doing Hong Kong - Beijing - Moscow by rail this September/October. I may post some experiences somewhere on Flyertalk if there is the demand, though 'Flying' isn't really the point.
East to West seems not to be the preferred route for tourism. With hindsight I would have probably gone the other way. A number of problems with the itinerary would have lessened or been totally eliminated.
I used CTS in London to do most of the bookings, but in keeping with the Flyertalk ethos will be doing some of the hotels and all of the flights with points/miles. Ian Tuton at CTS has been wonderfully patient with my requirements and changes to itineraries. Highly recommended for anyone booking from the UK.
The biggest disappointment so far has been how difficult getting onward rail from Moscow to the UK has been. You can't get the ticket issed in the UK, and you can't get a Belarus transit visa without a photocopy of the ticket. I originally wanted to go 'coast to coast' and cross Asia and Europe by land. Oh well.