One idea to try to keep everyone happy, how about having a checkbox for "default images to Corona Bitmap shader"? This way users can decide whether they want it or not?
With regards to speed increases, I managed to take the scene parsing value from 8 secs down to 4 sec, just by putting the HDRI into a Corona Bitmap, that's before I went through all the other images and changed those over, I think that got me another 1 second. Makes the IPR much snappier if you have to restart it.