What stopped you from using Linux-specific features before systemd? They were accessible from userspace well before systemd came along.
I was using some of them, such as kvm for my virtualization and lvm for disk management. But systemd still had a substantial 'oh, wow, Linux lets process management be this easy and powerful?' factor, showing me something new that I hadn't seen in my use of any other system (FreeBSD, OpenBSD, Windows, a touch of Mac).
I suspect its not well known because there was no commercial, marketing drive behind them. Nowadays at least one of these seems to be needed to even gain visibility. People don't go search what's cool/good where it is. They wait for HN or some other news website to tell them
Just like the regular news really. Turns out it doesn't work all that great.
Perhaps I'm ignorant and this was always possible.