It will be interesting to see what mutations come out of this among a very large population with relatively weak immunity. Especially after the Chinese New Year.
We will likely have to rely on China's excess death numbers to gauge how deadly this spread will be. China is now only counting deaths due to pneumonia and respiratory failure where COVID is the primary cause as COVID deaths. Fortunately China's excess death data tends to be robust. It will be delayed though, so we won't know how bad this wave will be for awhile.
This is going to be a humanitarian crisis for China. Many older Chinese are either unvaccinated or only partially vaccinated. And given the prior containment policies, there is limited population immunity outside of vaccination. China does not have much ICU capacity, so we may see Chinese hospitals being heavily strained.
This change in guidance is very restrictive compared to other health systems. The US CDC counts deaths where COVID was the underlying cause or contributed to the death as a COVID death- note contrary to some cranks this doesn't mean that a person that dies from a car crash, but was infected with SARS-COV-2 is counted, as COVID had no involvement in the death. This isn't a "with" or "from" COVID point. All counted deaths in the US are "from" COVID per CDC guidance.
Given the issues with testing and death reporting in general, excess deaths are often a better metric for the full extent of the pandemic in any case. As confirmed COVID deaths have generally underestimated COVID deaths across health systems.