No, I was thinking of an itinerary like Abroad -> Beijing (via valid entry point) -> Train that travels on a direct service but passes through areas outside of the TWOV area along the way -> Shenzhen -> Abroad (via valid exit point).

While I'd like to see data points to support this, would travel by high speed rail on a direct service be treated differently than flying?

Urumqi wouldn't be covered since not only is it outside of the 240-hour TWOV area, but it's not defensible to say that you were going between Beijing and Shenzhen by way of Urumqi.