I hope they don't bring back more Primarchs. We already have a narrative problem of too many Deus Ex Machina'd stalemate duels between plot essential characters who can't be killed off at the moment. Primarchs and even Abaddon should remain absent from most of the stories they tell and the focus should be on the myriad conflicts happening across the galaxy.
I dont like to see Primarchs everywhere. They should still be very rar. just one Primarch release per Edition would be okay.
I would prefer to expand, Focus and going deeper into the still existing loved characters like
Ahriman, Grimnar, Garadon, Helbrecht, Grimaldus, Khârn,...
But the problem is that with that approach, some will have their primarchs in a sane amount of time will others will not. 3 years per edition if we consider the time from 8th to 9th, so as we have one loyalist Primarch with two who are most definitely dead, that's 6 to go. So, we should see the last one in 15+ years (assuming we get one soon), eh? Nice. The problem is the same as with the separated chapters in general, some get their special dudes and some do not. Ultramarines already had a million named characters, and then they got a Primarch on top of it all too.
Now, I'm not saying to just plop all the Primarchs into the game just like that, it'd be a narrative nightmare more or less if nothing else, but regardless it's a bummer when some chapters get such things and others don't. Although of course it'd still always be a problem regardless unless they change the rules established so far, since if I recall correctly Guilliman only "works" for Ultramarines, but not their successors.