alt Hacker NewsYou will first probably need Congress to legislate away the long standing prohibitions against offering (easily) user-modifiable RF devices on the market.
Self ownership and full 'right to repair' has carve-outs in the FCC's regulations in the name of limiting unintentional broadcasting/radiation. Maybe a challenge to those would survive in the post-Chevron environment. I wouldn't expect any Congress in the last 25 years to pass a law which would go against the incumbent telecom lobbyist interests though, and I'd expect such a hole if it did hit case law, to get 'patched' fairly quickly.
About the only way to really solve that would be to embarrass vendors enough to open their moats.
I dunno, I'm pretty big on FOSS but I don't think you would need that to improve. Requiring that the firmware have its source code available to audit doesn't mean that users can replace it. AFAIK you could, today, with no legal changes, have a vendor release 100% of the code under eg. a MIT license while also making the device refuse to run firmware not signed with their keys. Researchers could poke at it to find bugs, and FCC regulations wouldn't be touched. (Note: IANAL, so feel free to point out if I'm wrong about that)
(To be clear, I don't think that's good enough; at a minimum I think there should be a wifi card that does refuse modifications and a main application processor that is 100% user controlled so that they can actually fix problems without needing the vendor to help, but I think it's useful to point out that auditing code doesn't require being able to install it)