I have already completed a study to see about replacing my SV-D1000 with the 12" HDX and you can make it fit with surgery and panel rearrangement. The biggest change will be cutting a relief in the F-1202B Panel Base to clear the case depth of the 12" HDX. That will require a reinforcing bracket to be added to keep the front of the panel base stiff between the longerons. I previously added a 1" AL angle about 6" behind the front edge of the panel base that runs from L-longeron to R-longeron as additional bracing for my IFD-540 navigator (11 lbs). You will also need to go to a one-piece panel because the center radio stack has to move to the right about an inch.
Here is a dwg file if you want to play with 12" HDX and RV-12 panel designs:
https://drive.google.com/file/d/13aDt8A6C2GUyMCfnS9QDZpAqCUjmutku/view?usp=drive_link
The lower portion of the HDX is angled out from the panel, so the 2D drawing can be a bit misleading as it projects forward of the panel base (stick clearance is not an issue). You will have to move the radio stack to the right, the F-1202JL/R instrument stack supports should be usable. I was also contemplating adding a Garmin D5 on the right side, which is where I currently have an iPad Mini mounted.
John Salak
RV-12 N896HS