Unfortunately I have no big knowledge of file formats and their “magic numbers”, and all RAW processors I know of seem to recognise RAW files by their extension.
Also, some RAW files are equivalent to TIFF files, and actually GIMP sometimes passes TIFF files to the RAW loading plug-ins. PhotoFlow passes such TIFF files back to GIMP, but again this is decided based on the file extension. By the way, this is exactly what UFraw is doing since long (the PhF plug-in code is derived from UFraw) and nobody seems to have complained in the past.
I’m not saying this is perfect, but on the other hand file extensions do have some meaning…