The direction indicator is gyro based rather than magnetic so for most GA it would probably be enough to just learn the offset for the area you are flying and add that when you set/check the DI.
For VFR flying it hardly matters anyway
For VFR flying it hardly matters anyway
Edit: Just read here that in the pacific Northwest of the US there is a 20 degree deviation! I had no idea. Where I flew it was a degree at most.
My point was that this shouldn't require any instrument upgrades to the GA fleet