The Space Wolves
Thunderwolf calavry + wolves - now my thoughts here are that the thunder wolves are supposed to be the biggest wolves around and the marines look like jockeys riding througher breads not grown men riding Shetland ponies. So unless they come up with new and improved primaris thunder wolves I don't see how this will work. The ferrisian wolves as just normal wolves and will continue as before.
Grey hunters - I guess this is fairly easy, just alter the weapon loads of the intercessors and call it job done.
Blood claws - these boys are a lot harder to do. With the apparent loss of scouts, will these turn into space wolf style reivers? Trouble is blood claws are very different to scouts, in both form and function. If they are replaced, it will have to be with a dedicated unit, but does that fit in to the new scheme?
Long fangs - these are basically just devastators with some extra fluff, so they'll just become aggressors.
Stormwolf and Stormfang - I guess these will stay roughly the same but just get the usual primaris treatment, ie bigger and more powerful, otherwise they might just be replaced with the generic flyer.
Wulfen - if I remember right, these guys technically can't change at all as they are the 13th company? So I guess they'll continue unchanged, but just be a little less special.
Skyclaws/swift claws/wolf scouts - I've lumped these together as they will all just end up being replaced with the new versions, in the case of skyclaws the inceptors and the wolf scouts with reivers. The swift claws will have to wait until they bring out the new bike units.
Wolf Lord - I guess this will just become the captain model with extra fluff for the background.
Rune priest - both librarian and apothecary in one. The question is, will this receive a new model or just use one of the other models with some extra rules? Personally I lean to the latter more than the former.
Iron priest - the wolves version of the techmarine, and as with the Lord and Priest, I think it will just be a case of same model, extra rules.
Next up are the Dark Angels, there are still quite a few unique units here too.
Interrogator-chaplain - this is probably the easiest model to do, just the regular chaplain with a few extra rules.
Deathwing (including the knights + command squad + terminator's + dreads) - most of these units will probably just take on there primaris equivalent, namely the aggressors and the dread. The only units that may have issues is the knights, as they have specialist weaponry. I can see these guys becoming a normal unit with lots of extra rules rather that a specialist unit will a few extra rules.
Company vets - again I this k these guys will go to be hellblaster (and equivalent) units, loosing some of the versatility but still keeping the veteran type unit.
Ravenwing (including black knights + command squad + bikes and attack bikes) - as with the Deathwing, lots of these will be replace with the primaris units, what ever the bike unit will be called. As with the vanilla marines, I see the attack bikes disappearing and I can also see the black knights loosing some of the special weapons (aka the talons) and becoming a normal unit with extra options, mostly combat ones, and gaining lots of extra rules.
Landspeeder vengeance - with the fact that I see any replacement for the landspeeder becoming bigger and better armed, the vengeance becomes less special and looks less necessary. As such i can see the vengeance disappearing in favor of a normal speeder with extra weapon options and rules.
Ravenwing darkshroud + dark talon - these are two very specialist units, used only by the Ravenwing and no one else. As such I'm not sure that they will be replaced. The dark talon might be replaced, along side the jetfigher, with the generic fighter/transport flyer from the vanilla marines. It would probably get extra rules, similar to the rest of the Ravenwing but that would be it. The darkshroud will have an even harder time I think, as with the vengeance, due to the increase in size I see from the speeder. I can see this unit becoming a normal speeder with extra rules but little else if it exists at all.
Nephilim jetfighter - as I mention above, I can't see this existing I current form. If they do bring out a primaris fighter, then it will get a black paint job and some extra rules, if they just release one flyer, then it will still get a black paint job and some extra rules and be the new jetfigher.
The final chapter to talk about is the Blood Angels. There are less unique units here but still a few to talk about.
Sanguinary priest - this is the only one
Librarian Dreadnought - I can see this becoming a new unit for the primaris units in general, being opened up to a lot more chapters, after all why is it that only the BA can make Libby dreads?
Furioso dreadnought - again, I can see this unit being opened up as an option to other chapters in the new dread model.
Death company (Dreadnought + troops) - well, this is a difficult one. With the changes made to the primaris geneseed, has the flaws of the chapter been eliminated? Only time will tell if the death company will continue to exist or if the flaw has been eliminated, personally I think it would be a mistake to eliminate the flaw as its part of the the chapters lore and so ingrained into the chapter. Hopefully it will remain, as all it requires is some extra rules and doesn't really require specific models.
Sanguinary guard - these guys are very different from pretty much everything else, but I see these guys becoming inceptors with extra options and rules. Loosing some of there individuality but retaining some flavor.
Baal predator - as this is pretty much a normal predator (or repulsar as it will actually be) with a different gun, I can see it continuing, but I also see it being opened up to other chapters, the same as the dreads above.
So that's the end of my little run through, ok, so its very pessimistic and will in all likelihood be completely wrong. I hope that all the current units will get ported over some how, but I very much doubt that they will. As is probably evident, I see quite a culling of units, especially in the short term, as this gives options for new units and releases in the future, without having to come up with "new" units. Its also quite a pessimistic view in the fact that it makes no allowances for the continued existence of the old marine. Why? Well if you had the choice between turning a recruit in to an old style marine or a primaris marine, would you really make the old one? Of course not, you'd make the bigger, better and more powerful version. And with the current state of the wh40k universe, losses are going to be high and lots of replacements needed, so the old marines are defiantly on borrowed time.