First, we have a problem as we need to support what's out in the world.
How about I write a patch to change the decompression call in fit_image_load() to fall back to a memcpy() if the decompression fails (and print a big warning that the FIT image is wrong and should be updated)? That should keep those old installations working.
Second, what is intended with what's out in the world? Indeed before we didn't do anything with the compressed data. But now what, we're saying it's compressed, but not providing enough details to U-Boot to uncompress it?
Hmm... I'm not sure why it wouldn't just decompress correctly, actually. Is there anything special with how gzipped data is formatted for the kernel decompressor? Or is there any limitation in the U-Boot gzip implementation?