The requirement for ADF won't be taken away as long as NDBs feature in published procedures
I wonder if those two issues are even connected... ?
The ADF requirement is only for IFR in CAS, but there are loads of ILS, VOR and NDB approaches in Class G.
Why on earth not simply authorize GPS overlay approaches
They are
not illegal
now. As a private pilot, you can legally fly a VOR or NDB approach using a GPS. Only AOC operations, with an approved procedures manual, may specify what equipment should be
used in a given situation.
Most pilots fly NP approaches using a GPS... usually using the OBS mode because many overlay procedure depictions are less than complete, or the depiction is somewhat confusing when related to the Jepp plate.