With Ubuntu 18.10 being the release after an LTS cycle, it's shaping up to be another big feature period. They have already been discussing Zstd-compressed Debian packages for Ubuntu 18.10 while the latest proposal for this next cycle is on switching from Gzip to LZ4 for the default kernel initramfs image.

Canonical's Balint Reczey is going to be adding support for LZ4 compression to initramfs-tools, which should be done in time for the 18.04 release, but for the Ubuntu 18.10 release is where they are looking at making the LZ4-compressed image the default rather than Gzip.

The LZ4 initramfs compressor yields a slightly larger file size, but significantly quicker decompression/extraction over Gzip. On one test system, this shaved about one second off the boot process for the time to unpack the initramfs.

LZ4 for initramfs on Ubuntu is now being discussed via this ubuntu-devel thread. We'll see if that happens for Ubuntu 18.10 as there is also work on adding Zstd compression support for the kernel image too, which may yield even better compression vs. speed ratios and could in turn end up becoming the new default.