Agreed, and I've also seen two (anecdotal) reports that many GF3 employees didn't travel back home for the lunar new year, as a precaution, and that Tesla GF3 has introduced new, stricter health measures at the factory.
If the quarantine of Wuhan works we should see a peak in new cases and a drop-off in about 1-3 weeks. Even if Shanghai introduces new containment measures, the road traffic of supplies would be among the last impacted, because that's how food is transported too. To not throttle economic activity while maximizing containment must be a top priority of Chinese officials.
If things get worse there will be early warning signs, such as more major cities quarantined.
Update, this just got announced by the Shanghai government:
Global Times on Twitter
"
Enterprises in Shanghai should not resume work before 12 pm on February 9 and
all kind of schools including universities, high schools, primary schools, vocational schools, kindergartens and nursery schools should not start the new semester until February 17: Shanghai Government"
I suspect "enterprises" includes GF3 too.
The Lunar New Year ends on February 2, so this is an at least one week extension for businesses, and an at least two weeks of shutdown of schools, kindergartens and universities.
Next steps would be restrictions of road traffic (long distance bus traffic got stopped yesterday already: this is the cheapest and most common form of transportation used by migrant workers), and the banning of inter-provincial travellers from entering Shanghai.
Again, like in Beijing, these are well choreographed, aggressively proactive containment measures - very different from the SARS reaction which was slow and reactive.
China's primary strategy appears to be to ride it out in Wuhan via a full quarantine, and to slow the spread elsewhere via clever use of the Lunar New Year, where people are at home among family and friends in relative safety. By prolonging the "vacation" they take the edge off the disruption and also make sure people relying on wages to sustain themselves aren't trapped in big cities without sources of income.
Previously I didn't understand why China waited for people to travel for the new year festivities (because this was a transmission risk) - now I'm reasonably certain it was intentional to depopulate big cities voluntarily while infection levels are low, and move workers back home to relative stability, and that most of this was part of a systematic, proactive response.
But I could be wrong, and it would take time for the markets to realize this and stop panicking, so this is not advice.