The second phase of planning goes directly to Pinggu.
Mapo and Niu Shan definitely have light rail, and the other one is S6, which comes from Yizhuang and Tongzhou and connects three key new cities. The current planning scheme has not been finalized yet, and the time is not in the "three rings, four horizontals, five verticals and seven paths" planning circuit diagram of 20 15, 19, 56 1 km. Therefore, the S6 line, another possibility is the current airport light rail L 1 line. Shunyi strives to extend from the Capital Airport to Shunyi City, and then directly connect Ma Po and Niu Shan to the north. However, this is also a bottomless thing. The Capital Airport is very uncooperative and may not be at the bottom of S6.
Because I pay more attention to shunyi new town and light rail at work, I basically know the most official data. I hope it helps you.
One thing is certain: Mapo and Niu Shan will definitely have light rail, but 20 15 is definitely impossible.