First off, I understand that one can have their own interpretation of a RTW trip. The circumfrence of the globe is just shy of 25k and while the trip you mentioned is not technically around the "fattest" part of the globe it is very much indeed a RTW trip.
I completed a very similiar trip to what you mentioned last year and rode almost 23k over the course of 3 and 1/2 months. Some might say thats quick, some might drop their jaw when you say you split for over 3 months. Depends on who you talk to right????
I went from Japan to Vlad, west through Siberia, Mongolia, then eventually south to Turkey and up the adriatic, through Europe, Ireland Scotland and back to Canada.
I have also done done Colorado to Patagonia 2 years before that and while it was not the same trip, it was part of one great journy to see the world. What im getting at is that I think it suffices to say there are more then one way to do a RTW trip. It does not have to be continuous, do the parts you can when you can and keep the dream alive as you go back to work family, or whatever brings you home.
The route you mentioned is a "common" one for several reasons. Right now the reasons include the extreme difficulty of getting into China with a bike. If you wanted to go due west from Vlad... and getting through Afganistan, Pakistan, Iran, Iraq etc if you wish to ride further south through SE asia and India.
I did not bring much money (because i dont have much money) and was able to get the trip done for under 10k usd. Not including my bike, parts, gear etc, that I already had. I camped ALOT, ate cheap, was stingy with my money but it was great......
Dont forget that there is also a realitivly small weather window to get through Siberia and eastern Russia. You cant really spend 5 months in that part of the world with out running into snow, flooded rivers etc at some point.
I am more then happy to give you advice, recomendations, anything at all, if you get closer to making it happen. My only advice right now would be to just do it. Not to sound like a nike ad but its true. You will not regret it i promise that.
my email is firstname.lastname@example.org
is you have questions feel free to send me a line.