I am gearing up to ship a small first step of Private Network Access [1] in Chromium. Roughly:

Websites served over HTTP from public IP addresses will no longer be allowed to make subresource fetches to private IP addresses (RFC1918 and/or localhost). Specifically, this restriction applies to non-secure contexts. Secure contexts are unaffected by this change.

We have metrics in place telling us that ~0.1% of page visits at most make use of this feature.

I am interested in WebKit's opinion on this matter. 

For more details, see the chromestatus entry [2] and the Intent to Ship thread on blink-dev@chromium.org [3].

Cheers,

Titouan

[1] https://wicg.github.io/private-network-access/

[2] https://chromestatus.com/feature/5436853517811712

[3] https://groups.google.com/a/chromium.org/g/blink-dev/c/cPiRNjFoCag/m/DxEEN9-6BQAJ