The Garmin 1040 have a feature, which showing endurance/potential during a ride.
Is it possible to ad this as a chart, so I can see it at a glance in Intervals?
Do you have any info on what that actually is? If it ends up in the fit file then in theory it could be plotted. But it does depend on the background and science behind it. You can try opening one of your ride files on fitfileviewer.com and see if it is there.