You're right that we can't advocate for just eliminating copyright, without shooting ourselves in the foot. However, eliminating copyright, combined with, say, an obligation of software companies to disclose the source code of their "products" to their customers, or, less intrusively, with making the type of NDAs you describe illegal, would work.
Its one of the defined software freedoms of the FSF, after all, and its fundamentally why software freedom is advocated for, but it absolutely doesn't need copyright to be enshrined in law.
We currently have both a draconian IP regime and woefully inadequate right to repair, but fixing the latter does absolve free software from needing the former to function.
It is a very different strategy than GPL, and doesn't look very likely to happen given the trend in both EU and US, but I see it as a valid long shot strategy. It would be a terrible strategy however if we gave up GPL without anything in return.