community VS mkroot

The Kiss Linux repos are not outdated, just the "official" one, there is one that is actively maintained by the community. https://github.com/kiss-community/community.

Yes. The init scripts are written so as to be as init-agnostic as possible. See here to see what has specifically been tested. You'll need to either change what owns /sbin/init or, when configuring the kernel, change what executable it spawns as PID 1. Depending on what init you use, you may have to set up a service manager or gettys manually like this -- custom scripts are placed in /etc/rc.d with self-explanatory suffixes .boot, .pre.shutdown, or .post.shutdown.

back is packaged in the community repository: https://github.com/kiss-community/community

If you use the Official unofficial community repository, watch out for packages that might get dropped by maintainers.

Again, if you had bothered to read the sidebar you would have seen links to both the community site as well as the community github repo.

I am very exited for https://kisscommunity.org, the possibilities are endless!

Kiss linux is what you are searching for

This might not be exactly what you are looking for but KISS linux (https://k1sslinux.org) is a distribution that doesn't force ANY init on you, supports disk encryption ofc, it's probably the most light and minimal distribution out there (the core install has 7 packages), it's rolling release.

From mkroot page:

  https://github.com/landley/mkroot

Rob Landley's mkroot is about as barebones as it get. Compiles about as minimal system as possible that can boot under qemu. https://github.com/landley/mkroot

mkroot is about as simple as it gets.

Rob Landley's mkroot is a about as simple as it gets to build a system, it's now part of toybox.

$ git clone https://github.com/landley/mkroot.git

I don't endorse NixOS because I place high value on Unix conventions, but this is certainly an interesting write-up. Also take a look at mkroot.