You will only see Gen 3 characters in the Autofit dialogue if you bought some of the ‘iconic’ shapes for Genesis. I bought the David 3 shape, so it appears in Autofit for me. When you buy some of the iconic shapes from the store, they come with a ‘clone’ for Autofit.
So, really no update to Autofit itself as far as I know.
I found it’s pretty good to this is a M4 set, Celestial Armor by Valandar.
Autofitted to M5 and a really extreme shape of Sabbatic Goat the JCMs are being auto generated to even on custom shapes.
But you do have to look to see if the auto generated one are helping or not and may have to turn them off.