There are a few additional hurdles to overcome from the Airports' perspective
Not just from the airports' perspective. Our GNS430 is perfectly capable of supporting a GPS approach -- no physical mods required. However, there's a placard that prohibits its use for GPS approaches. To remove the AFM limitation requires a major mod performed by a Part 21 Design Organisation (which the original installer isn't). So just for the paperwork for one aircraft, we're looking at a four-digit sum.