I like your idea because I could see the Chinese government doing this to help prop up SMIC too. The RPi4 isn't any smaller than 16nm, and SMIC needs 14nm customers.
Shoot for the 500MHz target listed, which is achievable with Victorian era style over engineering. Next sell those more or less at cost after the government footed the bill for initial capital (probably paying back .gov.cn first). Then using the massive body of software you expect from the new ecosystem around the first wave of chips to reoptimize the cores and inch your way towards really competitive chips. All the while SMIC gets great experience at their lower node with a pretty low risk, but high volume project.
Total speculation, but fun speculation. If someone pulls that off they probably win the whole Made in China 2025 thing for homegrown computers in an interesting enough niche to have a foreign audience too.