I think the proposal is from someone thinking along the lines you've expressed earlier - i.e., that people should not assume that regions outside the 'safe zones' do not contain cables. The intent is therefore to limit the extent of areas that can be considered as 'safe zones'.
As you say, outside of 'safe zones' is not, and should not be considered to be, necessarily free from concealed cables.
However, it is at least the case that
inside of 'safe zones' one has to assume that cables may well be present, so that greater caution is required (if one has a drill, screw or nail in one's hand). I would have thought that this would be an argument for
extending, not reducing, 'safe zones'!
However, one problem is that the UK regulations require onerous cable selection/installation if the cable is not within the specified 'safe zones'. If, per what you say, the extent of 'safe zones' were reduced, but with those other requirements still in place, that would have a major impact on cable installation.
Although I know (per you recent post) that you appear to have an interest in further reducing risks that are already incredibly small (and although there have been one or two high-profile cases), do you actually believe that penetration of buried cables results in 'significant' harm?
Kind Regards, John