To answer my own question now that my trip is over...
There was an additional restriction of "not having traveled outside of China in the last 40 days 14 days" (I thought I heard “40 days” but it was probably “14 days” in hindsight; they sound similar in Chinese: 十四 vs. 四十). I boarded the plane at Beijing Daxing airport and they took me aside and ...
Unless you're a Canadian citizen, permanent resident or a resident visa holder, the answer is no. As per IATA's special COVID page:
Passengers are not allowed to enter until 30 November 2020.
-This does not apply to:
nationals of Canada;
permanent residents of Canada;
passengers arriving from the USA traveling for a purpose other than ...
Question: Are there additional restrictions on domestic flights within China due to COVID-19 in November 2020?
No unless your departure area is medium- or high-risk.
https://www.china-briefing.com/news/chinas-travel-restrictions-due-to-covid-19-an-explainer/ (mirror) (published on September 23, 2020):
Similarly, from March 28, all international flights to ...
Are these requirements even doable?
Yes if your area has decent COVID-19 testing facilities.
As JonathanReez mentioned, PCR results can be obtained within the same day.
The same applies to anti-body tests, e.g. from https://www.fda.gov/consumers/consumer-updates/coronavirus-testing-basics:
PCR tests take a few hours to process, so 48 hours is more than sufficient if there aren't bottlenecks in the test lab. For example, a Seattle company called Atlas Genomics advertises the following:
We provide travel testing with same day results. Please call xxx.xxx.xxxx
Atlas Covid-19 tests are being accepted by Hawaii due to our partnership with ...