(...) and would accomplish . . . what exactly?

It would move China's adversary further from its shores. Just like how America doesn't like Cuba being right there, with its rival politico- economic system, China doesn't like Taiwan being right there with its rival politico- economic system.

China wants TSMC

I agree that they want TSMC, but I think Taiwan's semi conductor disablement plan has more to do with guaranteeing international support for Taiwan than reducing the incentives for Chinese annexation of Taiwan.

What I mean is that Beijing can't say to the world "this is an internal disagreement that doesn't concern you" because if TSMC goes up in smoke the global economy is going to bottom out, it concerns everybody's economy. The fact that Beijing can't just seamlessly assume control of Taiwan means that the international community will not support that ambition. It's like Real Politik, but with semiconductors.

Ironically USA initiatives to protect itself from the vulnerability of Taiwan by (re?)patriating chip production will be bad for Taiwan's security... if they ever actually manage to rival TSMC's Taiwanese production. I say this because it will demote the conflict from one of global interest to just regional interest.

But that's all just my arm chair speculation, I don't actually have any idea what I'm talking about.