Looks like the railway is being extended to include the potential new location for LEGOLAND Beijing.
Source: http://news.sina.com.cn/c/2020-01-12/doc-iihnzahk3536616.shtmlThe suburban railway sub-center line will extend west to the Yamenkou and then south to Fangshan, and the Liangchen Railway will hold the sub-center line. Legoland may settle in Fangshan, and Beijing may use Liangchen Railway to provide high-volume rail transportation services for the Legoland project.