We currently grant full access to DConf which is not ideal. The idea is we have a proxy service that limits DConf reads/writes to a specific app-id. This has overlap with the Flatpak project: https://github.com/flatpak/flatpak/issues/78
Is this obsolete?
Yes xdg-desktop-portal grew a Settings portal that replaces GTK's usage of DConf so we removed the permission. Custom web extensions will just have to avoid using DConf if they do.