Straying away from shoes but staying with the universal fit theme...
As an exercise I used the shrinkwrap modifier to produce a version of the Average Male that has a more regular mesh structure around the waist, but has nearly identical shape as the existing Average Male.
If I were to do the same for the Average Female then one could automatically refit clothes that have been fitted for females to fit males. Just take the clothes fit to the Average Female, substitute the normalized version, which has the identical shape, rerun the fitting algorithm, apply the regularized female to regularized male target, and the clothing will fit the regularized male. You can then sub in the existing male, which has the identical shape, and rerun the fitting algorithm. A bit tedious but it could be automated. Ideally of course the default meshes would be regularized and then you wouldn't have to do anything, the fit would automatically tranfer between genders. But to do that you would need to go through a similar procedure for each of the existing targets to produce targets that have the same affect on the regularized mesh as the current targets do on the current mesh.
And of course I have only addressed the lower half of the body, dealing with chest features is a whole other story.
The same could be done for feet, if you look at the feet as you slide the gender slider back and forth you will see that there are a lot of gratuitous changes to the mesh between male and female. Those should really be eliminated. Except that would break backward compatibility.
Ah, such are the complications of life.