Forget fast four, would any tournament or event think of tinkering with current rules e.g. one serve, balls to last longer than 7,9 games etc. Takes out the serve bot factor.
Tennis was fine before Fedalovic & Serena started goating. There was a period 3-5 years back when the early 90s gen was a bit sucky and the future was starting to look a bit vulnerable, but in the last few years the mens and especially womens game has rebounded and flooded with plenty of interesting young stars.