We are not sure where you folks are getting your info, but it is dead wrong.
FreeBSD users will still be able to boot into Plasma with any other login manager that works on FreeBSD, including SDDM, which is upstream from Plasma anyway.
Linux users will just have one more option.
Plasma has no hard systemd dependencies.
We honestly don't understand where this is coming from. You will always be able to boot Plasma from whichever display manager you want... As you always have been able to do.
Someone just made up KDE would somehow block (?) other DMs based on nothing (which, by the way, sounds like more work than just leaving things as they are), and you believed them.
@kde thank you, again.
Sigh: <https://forums.freebsd.org/posts/740074>.
On the plus side:
― <https://lobste.rs/domains/lunduke.substack.com> fell silent in 2022
― <https://lobste.rs/domains/lunduke.locals.com> an explicit ban.

I want to clarify something first. I'm not saying that KDE Plasma should be the default desktop environment on FreeBSD nor that it is or it will be the default desktop environment. But, as part of the laptop initiative, the FreeBSD Foundation selected KDE Plasma as the desktop environment...