I just don't see what mechanism could be instituted that would work.
I got a great job out of college with a salary that was 20% higher than other graduates because I demonstrated I had a greater value than the other graduates (significant experience, passion for the field, demonstrated ability, etc).
Eventually the 600+ employee company was sold to another 600+ company that had rigorous salary/pay tables based solely on experience since graduation, and all the employees were ultimately forced into the pay grade scale. I ended up being paid less than employees who were obviously less proficient but had more time under their belt since their graduation. (it was slightly more complex than this, but the point and result is the same)
But I can't complain because there's no easy way to quantify my value in an objective way that's fair to everyone.
Similarly, there's not going to be an easy way to determine if a given employee's value - male or female - is actually on par with another employee's value except in a rather subjective way. This is especially true outside my industry. At least in engineering you can objectively evaluate how cheap a design is, how quickly an engineer completes the design, and how much maintenance the design needs in the long run.
There are some things in each industry that can be evaluated, but then there are the once in a blue moon problems that would only be well solved by someone that has significant knowledge and experience that can't be easily measured by monthly output reports.
Further, once you tie pay to a measurement system employees optimize for that system, which is one of many reasons why so many companies implement a rather subjective evaluation mechanism. IBM started tracking how many lines of code programmers wrote each day, and suddenly it became a race to write the lengthiest, most bloated code one could manage. Another company implemented a bonus for each bug fixed. Suddenly the number of bugs created exploded - and the fixes followed right behind.
So on the one hand you can average all the employees in a given position and force the outliers - both high and low - into the same pay scale to make sure there's no gender gap, or you can implement a complex system of objective measures with unintended consequences to grade each employee.
Neither option works, and there are a million loopholes.
Take the first option - all you need to do is create a new job title with slightly different requirements for each employee. Analyst 1, 2, and 3. Junior Analyst 1, 2, and 3. Senior Analyst 1, 2, and 3.
It's going to be impossible for any court to properly evaluate whether an employee is truly as valuable as any other employee, nevermind the second loophole that the company may have only opened up one junior position, and hired the senior analyst into the junior position.
I don't see any measures that people have so far proposed working at all, nevermind meeting their intended purpose. It is more likely that people will work around it, or optimize for it, making the situation worse.