The decision, confirmed on the Ubuntu kernel mailing list, isn’t exactly a major surprise: Ubuntu 20.04 is the next Long Term Support release of Ubuntu, and Linux 5.4 is the latest Long Term Support release of the Linux kernel.
Both receive on-going support for many years — so there’s a long term synergy, if you will!
Arguably there is just enough time between now and the release of the ‘Focal Fossa’ for Canonical’s crack team of kernel devs to prepare, package and ship the 5.5 kernel — but Canonical would also need to commit to support it for five years (support from upstream kernel developers ends in a few months).
So it’s arguably far less effort — and not to mention less hassle — to use an LTS Linux kernel in an LTS distro. Linux 5.4 LTS is maintained until 2021 by kernel developers, meaning the “patching critical flaws” burden is shared out.
“We are building the Focal / 20.04 LTS kernel based on the upstream 5.4 kernel. We have a version of this Ubuntu kernel in the -release pocket and continut to iterate and update it regularly while working towards the 20.04 release date,” writes Canonical’s Brad Figg.
Don’t forget: folks will be able to upgrade to newer kernels on Ubuntu 20.04 LTS. The Hardware Enablement Stack (HWE) provides back-ported kernels from newer Ubuntu releases to LTS users, at regular intervals.