How do you see firmware becoming more open without copyright exactly?

I'm no fan of imaginary property, but you're going to have to lay out your reasoning here. Firmware security is such crap precisely because most hardware manufacturers see it as nothing but a cost center they wish they could avoid.

The difficulty of installing OpenWRT or Linux in general on hardware comes from that hardware not being documented, or not having straightforward APIs like BIOS/EFI.

Or for some devices, community distributions that dubiously remix manufacturer-supplied binaries are available. But we generally see that as soon as the manufacturer stops their updates, the community versions start lagging behind as well.