Sure, there's nothing mystical about Shenzhen, and I'm sure it can be replicated elsewhere -- but on a decadal timeframe at best.
There are many different factors which go into producing such an ecosystem. Raw number of STEM graduates is a very crude proxy, but it's probably as good as anything else for representing the "feedstock" of such an ecosystem, and gives an rough indication of how difficult the task might be.
China produces ~8x as many STEM graduates as the US. Therefore, all else being equal, if it took China 20 years to develop such an ecosystem, it should take the US roughly 160 years to do the same.
"But wait!", you say, "The US can be a fast second-mover, learning from Shenzhen and not repeating its mistakes. Plus, we may have fewer STEM graduates, but on average they're better-educated and more entrepreneurial, which would allow us to move even faster". (Note, I'm not endorsing these claims, just saying that it's an argument one could plausibly make).
Fine, granting all that, let's say that each American STEM graduate is worth 10 Chinese STEM graduates. In that case, it would only take 16 years to begin to compete with Shenzhen.
That analysis is almost certainly far too generous towards the US, however -- and even if it were well-founded, what American politician would pursue the necessary policies, given a best-case 16-year ROI? And what American polity would accede to the requirements of such policies?
Answer: none. This just isn't going to happen in the US. India has the scale to pull it off, but not the organisational capacity; Germany has the organisational capacity but not the scale; most other places have neither. Anybody who thinks that it'd be easy to replace China is utterly fooling themselves.