As soon as two or more ladies start showing successful quads in their freeskates, then there will be a push to change the short program rules to allow it there. I can't see the ISU defining a required SP element to include something they have no reason to believe anyone can do.
I was surprised they allowed the 3A in the ladies' SP as soon as they did. But that was after Asada (and long before her Ito and Harding) had proven it possible for ladies to do 3A+2T combinations in the SP, so using the 3A as the solo axel actually made it easier to include 3A in the SP.
To add a quad to the SP, a lady would need to be able to do it in combination or to do it with preceding steps or other skating moves. We haven't seen that from any lady in a freeskate ever.
A quad will be much more valuable to ladies in the FS than in the SP, because even if they land it on one foot in the SP, if it isn't in combination with a double or triple jump the GOE will be -3, or if it's planned as the solo jump but doesn't have preceding steps the GOE will likely be negative even if the landing is good enough to get positive GOE in a FS.
I was surprised they allowed the 3A in the ladies' SP as soon as they did. But that was after Asada (and long before her Ito and Harding) had proven it possible for ladies to do 3A+2T combinations in the SP, so using the 3A as the solo axel actually made it easier to include 3A in the SP.
To add a quad to the SP, a lady would need to be able to do it in combination or to do it with preceding steps or other skating moves. We haven't seen that from any lady in a freeskate ever.
A quad will be much more valuable to ladies in the FS than in the SP, because even if they land it on one foot in the SP, if it isn't in combination with a double or triple jump the GOE will be -3, or if it's planned as the solo jump but doesn't have preceding steps the GOE will likely be negative even if the landing is good enough to get positive GOE in a FS.