It is developed but you have to use a distro that ship lxde packages or build lxde yourself. You can try xfce which is also light on resouces.
There are two problems with his solution:
When Unix was designed there were no yubikeys, full disk encryption, malicious actors trying to steal your data etc. Passwords and ACLs were just fine. So its is not that Unix (or a unix-like system such Linux) has a problem, it’s more like the use we do isn’t compatible with Unix’s design.
If we have a problem, why not do we create a universal solution for it? Because all things related to systemd are not about fix user’s problems, it’s about create “solutions” for Redhat’s corporate clients. It doesn’t matter if people find an use case for it or if the technology is interesting, it’s all about corporate interests.