I guess you'd want to be able to include it in your distribution. FreeBSD for example includes svn (or svnlite or whatever) so you can fetch/update the source and do a buildkernel or buildworld without having to install any ports.
> The FreeBSD Project aims to produce a complete,
> BSD-licensed operating system allowing consumers of the
> system to produce derivative products without constraint
> or further license obligations.
https://www.freebsd.org/internal/software-license.htmlAlso https://www.openbsd.org/goals.html and https://www.netbsd.org/about/redistribution.html#why-berkele...