Power curve comparison: current ride vs. PB envelope
For each ride superimpose on the mean maximal power curve, the portion of your overall mean maximal power curve of all your rides, relating to the same time period as the current ride. Us a different colour and dotted lines for the comparative graph. This will immediately allow one to visually rate how close to your envelope the current ride has been over any time period.

Great news, we actually already have this! On the Peak Power Chart, click the gear icon to access the chart settings. From there, you can turn on comparisons. For more information, please see: http://support.trainingpeaks.com/personal-edition/charts/peak-power-charts.aspx
Thanks for taking the time to share with us your ideas!