I don't play marines yet; I'm thinking of putting together a small force of them or even two small forces. My favourites are the Deathwing and the Grey Knights, but truthfully I don't think of either of them as space marines; I think of them as the Chambers Militant of the Inquisition.
Of the actual Marine marines, I prefer Dark Angels because I love the Deathwing and Ravenwing. Next would be Blood Angels because of their jump units.
What I have are Spacehulk BA Terminators, and Primaris Spacewolves from Tooth and Claw.
So that is my entire background in Space Marinology, so take everything I say with a huge shaker of salt.
But personally, I think that the whole Primaris thing has killer story potential, and the internal drama it could bring to a Crusade Force is insane. In October when Marines get their dex, I'm willing to bet crossing the rubicon is a Crusade advance for them, just like being interred in a Dread.
But it goes WAY beyond that. Like you could start with an Old Marine Force, and then fight a battle allied with Ultra Marines representing the Indomitus Crusade dropping off Primaris for everyone. Then they could fight as separate forces or detachments to represent the initial distrust between old and new. Set a threshold, like Old Marines trust primaris once they are blooded but not before. This way, Prmaris units have internal stories and politics themselves, because some will gain acceptance sooner than others.
Then HQ's can cross the Rubicon, which changes the dynamic again.
And if there are old marines that never trust, no matter how hard the primaris try to fit on, you've set the stage for chapter schism.
So. Much. Potential.
However, those of us who would drip the primaris into our forces to tell a story could still choose to do that, even if the minis were all released at once. That means the big release is probably the way to please the greatest number. I will say though, that since other non-Marine factions really need attention way more than marines do, drip feeding the marine releases allows the other factions to get the attention between marine releases.
One of the things that had me so upset when 9th was announced is that I was pretty sure it was going to lead to year long parade of stuff for marines with little to nothing for anyone else until year two, and quite frankly, the jury is still out. We can't speculate about the Codex release schedule beyond "There are two coming in October and one is marines, and there will be additional supplements, while old supplements will continue to work."
So if they can release a supplement AND a non-marine every month, we're okay. If they have to alternate though, that turns into the marine parade I feared. If the Codex/ Supplement releases are less than one/ month, all I can say is that the edition better last longer than 3 years. So many unknowns- it's driving me crazy, because we had learned the rhythm of 8th, and releases were easy to predict. Now everything is just questions.