I would rather say that the last case makes the most sense: the expected use case of loading a palette from a GIF is to display all the frames in that GIF (after loading them using jjANIMATION::load). In the last case, you can't do that, because different frames have different palettes. So maybe there needs to be an overload (or whatever) of jjANIMATION::load that imports the GIF frames as 32-bit (well, 24-bit really) sprites instead.

For the other cases, padding would probably be possible, though I'm leaving in that "probably" because I haven't taken a close enough look at our GIF library yet to know how it handles those cases.