Yes. It is true that you can patch the kernel against aufs, and also
there is an available patch from the Lzip project to add support of
lzip into the kernel, this support is currently limited for compressed
initramfs. Lzip won't work for the kernel modules, cause the support
is needed in the kmod side. There is one thing to do, request the
support of lzip in kmod.. which will be hard because they match the
available formats in the kernel, lzip was proposed to the linux kernel
developers some time ago, without an answer yet...
Always exist the possibility to make an unofficial patch. :-)