well... i wonder how much more there is to decode, since our brain images are nothing more than blurry blobs.
try to imagine a tree i.e., best pick one you are quite familiar with. how much details do you imagine? enough to create a sharp image? can you imagine the structure of the leaves at the same time you focus on the branches?
even though i believe every individual has a different inner view, i dont think anyone is capable of producing images in their head that anyone else can "read"... at max, we will be able to identify objects, maybe some faces, but it will be like interpreting abstract artworks...