I didn't consider Polytonic's point about the single track issue when I extolled the Washington Metro in my OP, but this definitely comprises a chink in the armor.

Moving on, following is a comparison between the DC Red Line and Shanghai Line 2:
-3 minute intervals (Shanghai) are preferable to 15 minute intervals (DC during non peak times)
-forward facing seats (DC) are luxurious; this will never happen in China
-Metro Center is leaps and bounds better than People's Square or Nanjing West Road for transfers; the latter actually requires people to walk as much as 1000 meters above ground!
-Shanghai Line 2 has stations at both PVG and SHA; this is a pretty big carrot for HBO people who don't mind being VERY close to strangers