Non-competes are mostly unenforceable in California. But you definitely shouldn't just sign one and assume it won't be enforceable in your case.

Assuming one did such a thing, would it be possible to take them to court and get a summary judgement that the clause of the contract is unenforceable and to be removed, so they can't use that as pressure against your new company as in the instance in the article?

It might be possible to commence a legal action for a declaratory judgement (a summary judgement is a different thing) on the matter (declaratory judgement rules vary by jurisdiction.)