Regarding Wayland, looking at this it seems that it might be pretty straightforward but then for example sway seems to be defining seats a little bit different. So it might require some tinkering in the end, depending which compositor you decide to use.
Loginctl seems to be X/Wayland independent and useful in both.
From what I’ve found it seems that there are more questions on the internet regarding something not working well in multi-seat or needing a patch for that, than how to set the multi-seat up. Situations like this usually mean that setting this thing up is quite straightforward. It might also be a niche, though