As an introduction to Devuan, please take a look at the systemd packages that are banned in Devuan. One is text and the other graphical:

https://pkgmaster.devuan.org/bannedpackages.txt

https://pkgmaster.devuan.org/log/unstable-banned.svg

That will give you an idea of the magnitude of the problem and how most of it is solved . . . it is sent to the trash bin!

Think about it: somebody who likes systemd might still be open to switching to another init system. Maybe they'll eventually change their mind about systemd, or maybe a new init system comes out that is (in their view) superior to systemd.

For this type of user, Devuan's patching is perfect, as it removes the systemd vendor lock-in that would otherwise force them to stay on systemd.

But as far as I understand, Devuan blacklists systemd entirely and prevents its installation. I don't think systemd itself has to be an enemy of init freedom, and dinit (which is functionally similar) proves this. So I think we could convince a lot of Debian users to switch over to Devuan if they had the option to use systemd without any hard dependencies.

TL;DR: many systemd fans can see that the ecosystem SURROUNDING systemd isn't futureproof, and would like the ability to use systemd today without being forced to use it tomorrow. Devuan could broaden its userbase by appealing to these concerns.