As stgraber pointed out in his article, shiftfs can also easily be implemented via dkms.
For those new to the concecpt of dkms, it let’s you install additional kernel modules without rebuilding the kernel.
Some time ago I set up a github repo for exactly this:
Basically the kernel module consists of one file shiftfs.c, which then gets compiled and installed.
By the way, for those wondering about packages for other distros:
Honestly it is a bit too complicated for me to struggle with the different package systems, approval processes, tests for each distro etc., but if you are interested in providing them, it is easier than you think.
You can start by searching for dkms packages on your distro and see how they are made.
Then you can use my repo to adjust the package files accordingly.
Additionally dkms also seems to offer options to create deb (format for Debian + Ubuntu etc.) and rpm (format for Redhat-based distros and Open Suse) packages:
Look for mkdeb and mkrpm in the manpage/documentation of dkms: https://manpages.ubuntu.com/manpages/focal/man8/dkms.8.html
Note: I haven’t tried this method.