This approach makes alot of sense to me. I may setup a second athlete and manually put in a TSS' amount for every ride and see how it effects my PMC. Since getting the power meter 7 months ago I have spent a lot of time trying to gauge how I feel vs my TSB. Usually its pretty accurate, but its only most obvious when the TSB is at an extreme positive or negative. The TSS' approach will make the easy rides look easier and the hard rides look harder so that will probably not change much other than to amplify the magnitude of the TSB curve.
I had never though of the TSS as needing to scale over time before. However, I have noticed that the 3 hours rides on the weekend are much tougher to recover from than the same day 1 hour lunch ride + 1 hour evening ride (even though the shorter rides are higher intensity and the TSS values are similar.)
Of course knowing there is a difference and knowing how to quantify that difference is not the same thing.