how many donations will you need to make a difference
A lot. If the Gov could force all the big companies to invest $100 Billion per year in a targeted manner (agriculture, SMEs, edu, sustainable Dev, infra etc), then that would make a sizeable impact to the poor and ultimately to the companies themselves in the long term, as people get richer from such donations
and will you keep forcing firms to donate?
Yes. Either donate normally or the Gov will destroy your business. Keep in mind that the Gov most likely wont force highly innovative companies to participate as they are crucial for China. Alibaba, Tencent, DiDi et al should all pay up though, because if they wont they will be in trouble
What happens when Xi exits
Xi has plenty of time at the top. He will likely go for a 3rd term as well. As such maybe by the time he leaves, the economic situation could be better and then start making these "donations" a law so that it gets formalised.
and a new administration comes with other priorities?
Dont believe western misinfo. Xi is not a dictator and as such, that this "common prosperity" decision was taken it means that there is a lot of supporters inside the CPC for this. I would also remind people that mid August, the top party leaders (Xi included ofc) went for an informal meeting, and immediately after that ended, the whole thing started.
This means that a consensus has been formed in the CPC, and I assume in the society as well, especially after Covid.
To conclude, the next administration, when that may be, will follow the same decision until another consensus is reached.
We should also be aware that Xi could try to insert that into the constitution (IMO highly unlikely), or make it a law at the end of his term (2027, 2032?) in order to ensure that the policy will be followed even after he steps down
There so called 'common prosperity ' should be addressed at the policy level by encouraging these internet companies to invest in foundational research, universities and start ups.
Ideally yes, but companies always try to do half-jobs and find loopholes. The CPC has left the details vague specifically for this reason. In this way, companies will try to ensure that they didnt make a low donation and so they will reach into their deep pockets and make a bigger donation than they would have planned without the policy being vague.
I expect that for this and next year this will be a kind of a pilot/trial and after the CPC sees the results it will move towards formalising the policy.