What, then, would it mean for the length of the match or the set if the number of points of at least five strokes doubled to two thirds of all points, and only one third remained at 0 ... 4 strokes?

Here I have presented in another thread

the no-deuce-rule which would shorten after six points the game still in progress, at 40-all, but not in such a fatal way as the no-ad rule.

These long games consist on an average of 10 points at the highest level. The no-deuce rule I use would be on an average about 8 points. And the no-ad rule would finish all the games right after the seventh point. It can be seen immediately that the no-deuce would reduce the time it takes to play overtime games and reduce the points played by an average of 20℅. However, the distributions of traditional point calculations are difficult to estimate "on an average"! The no-ad shortens to 30℅.

But what about the set if actual ball rallies would become more common in a thoughtful way? Number of strokes? Playing time?