I didn't met any universal generic solution for a train trip, unless much powerfull than Google maps. But if you need some specific info about Russian trains, here we go.
Most popular travel site to planning a trip is tutu.ru (in Russian), where you can find a first version of your trip via bus, train or plane. However, in English there is on Trains part of it.
For example, you can find a complete schedule for trains between Moscow and Irkutsk, with a complete route and station schedule for each of them (e.g., this is a google map for train
Route 003З Beijing → Moscow). This is a good start for finding a train operating over Russia, yet still not a perfect planning tool as it barely knows something outside the Russia.
Other thing that you can give a try is a RZD official site, main carrier in trains industry in Russia. There you can find a lowest prices for tickets, but the problem with planning outside the Russia persists. Other popular choice is OZON, but it's an reseller and have their site only in Russian.
PS: A couple of years ago I asked a question regarding such tool for whole Europe, you can investigate that too, maybe those sites know something about Asia trains too.