Since the Kobo appears to use some Adobe software internally I doubt that we'll ever see the entire source for the Kobo firmware. Kobo will almost certainly not have a license to distribute Adobe's code as open source. While they will have to provide Linux source code they will not be under any obligation to release all source code so I don't think the GPL requires them to release an SD card update.
I don't really understand why there should be any correlation between an SD update release and the release of patch files for any GPL'ed or other open source software on the device . . . . .
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