So often I like to see if I might get a PR for a workout, so I look at the total calories. If I convert the calories to Watts (simple divide by workout duration in hours, and then divide by 3.6) then I can see if the whole workout time will be a PR for that duration (assuming adherence to the power targets).
However, for time windows shorter than the whole workout, it’s tricky to work out, particularly with the complexity of some of the intervals. This would be a good motivator to know in advance that a PR is coming.
The UI might be similar for an existing completed workout… a compare button where you select a season or two to compare with a specific workout. Then it shows the same graph as you get when comparing seasons, but one of the curves is a prediction rather than a record.