Presumably the only way that this record could be significantly improved upon would be if Malaysia was connected to Indonesia (perhaps via the proposed Malacca Strait Bridge[0]) and then extended further if Sumatra and Java were connected (via the proposed Sunda Strait Bridge[1]). Beyond that, a rail connection from Asia to New Guinea or Australia is a lot harder to imagine. [0] https://en.wikipedia.org/wiki/Malacca_…
How about Lisbon to New York? https://en.wikipedia.org/wiki/Bering_Strait_crossing
It's not just the technical challenges of building a bridge or a tunnel in pretty harsh conditions. It's also that on the russian side there is a huge area that has almost no human settlements and no infrastructure. You'd have to build a train line through an area of nothing. That also means it's difficult to imagine intermediate steps (e.g. first building half the rail line to even get there).