Considering no one has posted information specifically about what would go into making this possible here it goes. Information from here:
http://wiki.qhimm.com/FF7/Field_ModuleDue to the way the decompiled files store the backgrounds. The easiest method of re-inserting them was to have the driver pull the picture from somewhere else. Instead what you would have to do here is:
A. Update the Palette section of every file to make sure you have absolutely every colour that will be used in the background.
B. Update the section that tells the driver how to put together the pieces (16x16 pixels) in order. Since the new backgrounds are 4 times larger. That means completely updating it or finding a way to tell the driver to use 64x64 chunks instead. And also that would still mean re-writing where the top left pixel of each chunk is since that would change from using the larger images.
C. Updating the actual background data with the new data and making sure every pixel grabs its colour from the correct palette.
Now I am in no way saying this is an impossible feat, I am only saying it will take a lot of work. But who knows, the members of this forum have always surprised me with their accomplishments so I believe someone will figure this out. I personally have been wrapping my head around this very idea since the re-release came out.