I can't tell if this is a legitimate inquiry or if you are just trolling with this argument.

Considering it changes nothing on what they actually work on on systemd I would give this a yes. Every time I hear "they will do this or that" it just never really happened. So far it feels more like "the boy who cried wolf" than "slippery slope" to me. But maybe I am missing something?

A lot of the devs have always here and there added features for secure/measured boot and image based OSes and things that make them more usable to daily drive (hermetic /usr/, UKIs, sysext, portable services, mkosi, DDIs, ...). A lot of the things make image based systems more modifiable/user accessible without compromising on the general security aspect.

If they really wanted to lock in Linux users to a single blessed image from them they would have had a better chance when Lennart was working at Microsoft (which generally is the only preinstalled CA) instead of starting a "competing" company (they are targeting a different niche from what I understand).

Can you prove beyond a reasonable doubt that they intend to force this on you without any way of disabling it, or that they have already done so? Because unless they plan to do this (and you have concrete proof of such and not just "well they could do this" claims) or they have already done it across a significant portion of the Linux distribution ecosystem (and no, distros voluntarily switching to systemd is not forcing anyone to do anything), this is fearmongering. Simple as that.