There's quite a bit of information, and some of it makes it a little clearer as to the origin and intent of these new Space Marines.
As you may remember from Gathering Storm, the Space Marines took an absolute pounding, with many Chapters under siege, destroyed or simply just lost - they needed a life line and the newly returned Primarch of the Ultramarines had a pretty nifty surprise to reinforce these beleaguered defenders of the Imperium - the Primaris Space Marines.
The existing Space Marine Chapters will get reinforcements, but thew exciting news is the formation fo whole new Chapters - and not just super-soldiers, these new Space Marines were created using the gene seed of the nine loyal First Founding Legions. Yep! LEGIONS!
Want a Space Wolves Successor Chapter? Well congrats, here's a way the fluff will give them to you!
The fluff now says that these new Primaris Space Marines have now occupied the deserted bases of the lost Chapters, taking on their heraldry and traditions. Think of this - the Crimson Fists FINALLY have reinforcements. Scythes of the Emperor and the Lamenters, so often the brunt of devastating attacks, now have some beefy troops to continue their crusade with.
This is a pretty cool addition to the universe. Having the untainted gene seed of the Legions to play with and adapt to your own custom Chapter? Have at it hobbyists!
Have a look at a few of the Chapters below - some familiar, some not, but a pretty damn cool opportunity to really be creative and add some of the existing bitz to these models and come up with your own idea.