Ill go through the list and see what's what, plus ill add in my pennies worth as well. At this point I'm going to say that these may not be the most coherent ramblings ever written but thats probably why I'm not a world class author!
So, HQ units;
Captain - well, we've all see this and know what the score is.
Librarian - yep, seen this too. Nothing has really changed in terms of model apart from the stat line.
Chaplain - I've not seen anything aboutthis apart from the transfer sheet stuff, but I can't imagine much will change again apart from the stat lines
Techmarine - now I've hear nothing at all about a Techmarine version of the Primaris marines, apart from the one on that new vehicle thing. So at least we know that there will be a Primaris techmarine.
The Elite units
Command squad (including an apothecary and company champion) - Ok, so this unit doesn't exist in the same manor as before but the component parts still exist. Now, I can't see a dedicated command squad appearing, as its essentially just normal marines now. As for the apothecary, again there are some transfers available and we've seen some artwork. As for the champion, well there is nothing yet, but I can see one appearing at some point. We also have the new Primaris ancient I this area ( either here or in the honor guard) taking over from the old standard bearer. I still not sure how there can be an ancient if they are all new marines!
Honor guard (chapter champion) - I can see some blinged up Primaris marines here, probably in some form of gravis armour. I can see these coming out with the Primaris chapter maspointThe chapter champion will I think be a Primaris version of the BT emperors champion.
Sternguard - now this is where things get a little interesting. Now, the way I look at it is that the new Hellblaster units are taking up this role, as specialist units. I expect to see other units, based on the same format as the Hellblaster but with melta or grav like weapons. Granted there not quite the same as the old Sternguard units, but they share the same sort of specialized hunting idea.
Vanguard - now this is a unit that I'm less sure about, I guess that there will be a Primaris version but I think it will take a different form. I think we will see a more dedicated combat unit here, with less overall options but more combat focused, along similar lines to the Hellblaster units, ie single weapon dedicated.
Centurion assault and Terminator's (both assault and shooty ones) - so this is the realm of the aggressors, a mash up of both certurians and terminator's. I have always thought of the centurions as a bit of a wet fish, a case of making a model for the sake of making a model and I don't see it being replaced. I know very little about the aggressors, but from what I've read and from what I think, these will take over both roles and in time we will see some more specialized versions, ie assault versions, armed with lots of short range and combat weapons.
Dreadnought (standard + venerable + ironclad) - I think we've all seen the pregnant Primaris Dreadnought, so I think we can safely say that things are continuing in the same vain, everything is that bit bigger and better, apart from the looks anyway. I think that we will eventually see venerable and ironclad version, even if they will have different names.
Now, for the Troops;
Scouts - and the unit that started all this off, the reivers. So there not billed as scouts, as technically there not scouts but fully fledged marines, more similar to the SW wolf scouts I guess, but to me they are the replacement for scouts. We may see a more scout like unit in the future but I doubt it, as the reivers do the job of scouts in a lot of ways, all except snipers really, but that can be easily rectified.
Tactical - intercessors, need I say any more?
So, Fast attack now;
Assault marines - I though we'd start with the easy one. The inceptors are the closest thing to assault marines at the moment. Granted, they have two big guns and no chain swords but they have a jump pack and funny shoes. These are the new assault marines and I thinkbwe will see some diversity soon, with some dedicated combat versions. Soon I think we'll see versions with big guns, the assault bolters plus melta, plasma and Flamer versions and versions with swords and shields, plus axes and mauls and probably claws too.
Bike - I defiantly see bikes, bigger, badder and better. I think they will either be more like one man attack bikes or jet bikes. As the new transport is a skimmer, I do see the Primaris bikes being skimmers too. So, one man skimming attack bikes then?
Scout bike - reivers on bikes? That would be my guess, if they show up at all, which is just as likely.
Assault bike - I'm not entirely sure we'll get Primaris attack bikes, as I think the main bikes will sort of fill this role anyway. We may get bikes armed with things other than bolt rifles or assault bolters, but a 2 man assault bike? Not convinced we'll see one.
Landspeeder - now this is a difficult one. With anti-gravity seemingly becoming more prevalent, I can see Primaris Landspeeders being a thing, possibly taking over the attack bike role somewhat as well. I think thenew versions will be more along the lines of the heresy era javelin speeders, with lots of weapons all over the place but I do see a unit very similar to the Landspeeder existing.
Were getting to the end slowly, but up now are the Heavy support choices;
Devastators - I can see a form of devastators but I think it will be more likely tied to the aggressors. A big mobile firebase, merging devastators and centurion devastators together to form a hybrid unit that's better than the originals.
Centurion devastators - see above, plus the entry for the assault version above.
Thunderfire -the old favorite. This has long been a long time and has remain unchanged for much of that time. I don't however see it getting an equivalent Primaris version. Like many things its so iconic, yet so old, both in terms of model and in game, that a replacement would mean a while new model and I don't see that happening.
Predator - I defiantly expect to see a version of this from the Primaris marines. With the new repulsor tank on its way, I don't think it would take much to get it to where it needs to be to be called the new predator.
Whirlwinds - I like these units, but in the new system i don't see much room for them. No, if ever a there was a unit that would be dropped it would be this one.
Vindicators - a deliverer of big pie plates of death, or not as it currently stands. With the loss of pie plates, I feel that these sorts of vehicles have lost their way. While I still think there pretty good, I don't see a new version. As with the whirlwind, I think delivery systems like this are dead.
Hunter and stalker - to be these two have lost out a lot. With the changes to flyers, these two have lost their purpose. No longer is skyfire required to hit flyers and while these two do gain some rules, neither will be replaced.
Next up is the Transports;
Landspeeder storm - with scouts effectively gone and replaced by reivers, so to will the storm pass quietly in to the night.
Rhino and Razorback - the repulsor is basically the new razorback and as with the predator, it wont take a lot to make it in to the new rhino. Up armed for predator, down armed for rhino, if indeed we get a rhino. The Primaris squads seem a lot smaller so there may be no need for a rhino equivalent.
Edit: with the new info from the warhammer community page, it appears that the repulsor maybe closer to a land raider replacement, or more likely a combination of rhino and razorback.
Drop pod - how can there not be a version of this iconic delivery system? There will be new pods, with new options. I have no doubt that this pod will be bigger and better and maybe even mobile, maybe....
Land raider (including the standard, crusader and redeemer versions) - the replacement of the raider will in some respects depend upon the rules for aggressors and whether they will fit in to the new rhinos/razorbacks. If they do then there is little need for a raider replacement, however, I suspect that they won't, in line with the current rules and so a new raider will appear. I think this will also be a grav vehicle too, as will allthe new primaris vehicle models.
Last but by no means least, the Flyers;
Stormraven - the transport flyer, I can see a new version of this, bigger to take account of the bigger dread and marines, but also better armed.
Stormtalen and Stornhawk - if these are replaced, then it will be with a single model, somewhere inbetween the two but no doubt with more guns. However, I more see the pair disappearing and being replaced with a new flyer, the same one that replaces the Stormraven. I see it being along similar lines to the deathwatch blackstar flyer, but bigger and more powerful. This is mostly due to the Overlord and Thunderhawk situation.
So that's most of the units covered, not in great detail but enough to put my thoughts down on paper. I think that overall we will see a reduced lineup of units for the new primaris marines over the old marines, at least in the short term. Some units down need replacing, as some are no longer required and some are duplicated. With the increase in stats of the new marines, so units also be come unnecessary, such as centurions. Of course, I could be miles out and be talking complete and utter bullocks.
Why I'm on a roll though, I'm going to look through the other none codex compliant forces.