Kyungsik Lee posted the set of four patches that add in support for LZ4 compressed kernels and the initial RAMdisk on x86 and ARM architectures. LZ4 is a lossless compression algorithm known for its extremely fast decoder. The kernel decompression version is based upon the implementation by Yann Collet in the lz4 package.
In early testing from an ARMv7 system, the LZ4 compressed kernel image was 8% bigger than the LZO image, but the win comes in the form of faster decompression. A test Linux 3.4 kernel with LZO took 301ms to decompress while an LZ4 image took 251ms. The LZ4 image was even faster if enabling unaligned memory access, where the time needed was only 167ms -- approaching the point of half the time that was needed for the LZO kernel.
These patches that add in the LZ4 decompressor module and other changes needed for supporting LZ4-compressed kernels on ARM and x86 architectures can be found on the Linux kernel mailing list. This would potentially be a feature for the Linux 3.9 kernel.