Optimize to file size in save for web and devices

Yes, something like what you are saying. The output should be saved in a specific size already mentioned in the script

A script can look at the save file size if not within the size required it can change the image quality and save over that file till it is what you want.  IMO file size is only important for slow Internet connections these days.  With good Internet connections and high resolution displays you want high quality images on the web.