I was curious if you ever looked into integrating the INS into the GPS or NAV CDI since the data is there DTK and XTK error.

When I said integrate into GPS what I was meaning was to replace the GPS input to the HSI such as Flight1/RXP GPS units do when you select GPS.  I actually think this would be an accurate depiction of operation of an INS unit.   So no custom gauges should be required, but then I'm not a programmer so I could be completely wrong. I just figured if they could do it with a third party GPS you'd be able Todo the same thing as the pertinent information is there. DTK, XTK error, distance etc.

I don't doubt you are wrong at all.  It has me wondering how RXP and F1 manage it with their third party GPSs.  They utilize the simulator CDI function to switch from Navaids to their GPS and totally disregards whatever the inbuilt simulator GPS says.  Oh well.

Cheers