I have been toying with the same idea for a few months now. The way I understand it is that you will normally recoup around 50%, so 50k of the 100k install.
My concerns are:
the NA g5 has come down quite a bit in price. They are offered now for 500k. So they sell for 475? An upgraded G2 comes to around 400-460k. The delta between the two isn’t that big anymore. For the extra amount you get a 2013 aircraft with GFC700, higher flap speeds, more useful load, etc. So is there going to be a market for G500 upgraded G2’s? Or will it be a small niche market? Look at the amazing upgraded G2 by Nexair with G500’s, 650’s etc. It has been on the market for quite a while. It’s currently listed for 460K. It’s an amazing aircraft but no takers so far.
What if Cirrus releases a NXI upgrade program for Perspective birds in 2 or 3 years (when Cirrus releases a G2000 based G7) Based on other upgrade programs the pricing should be somewhere between 28 - 50k. That a lot less expensive than the upgrade to G500’s. An upgraded G3 or G5 will actually then be “cheaper” than the G500 upgraded ones.
On the other hand you only live once and there will always be new technology around the corner. I absolutely love the g500 TXI + 750/650 combo. I feel it’s much more user friendly than G1000’s and it seems Garmin releases updates at least 2 per year.