Are the Russians going to eventually adopt the same track guage as everyone else? Whether or not an Alaska to Russia railroad ever gets built, there's also the Europe to China shipping problem...
Our track gauge (Canada, US, Mexico) is the same as most of Western Europe, but that is a far cry from everybody else.
Following is a list of places that use other gauges, just off the top of my head.
Thailand, Malaysia, Vietnam, parts of Bangladesh and India, and a few other places: 1.000 meters (3'-3 3/8")
Japan, Taiwan, Philippines, Indonesia, South Africa, New Zealand, parts of Australia and some other places: 3'-6"
Russia, Ukraine and most of the rest of the former Soviet Union" 1520 mm - really close to 5'-0"
Brazil, Ireland, parts of Australia: 5'-3"
Spain and Portugal: 1668 mm - really close to 5'-6"
Argentina, Chile, India, Pakistan, parts of Banladesh 5'-6"
In southern Africa, most former British colonies have 3'-6" gauge, most former French colonies have one meter gauge, most places north of the Sahara are at standard (4'-8 1/2") gauge
Otherwise, most places have "standard" gauge, including parts of Australia, and the Shinkansen lines in Japan.
Several of these places listed have some railroads at other track gauges than their main one.
Since India Railways carries more passenger volume both in pure numbers of people and passenger miles than anybody else, in fact I heard once more than all of Europe put together, does that mean that the whole world should convert to 5'-6" track gauge?