I'm emphatically against the DA codex being "rolled in" to vanilla. For one, we tend to get the codex that sets the standard for the later vanilla codex; not the other way around. We tend to pioneer the stuff that gets a revision and incorporation for the vanilla dex; plasma cannons being one example. We could fairly be called the space marine test chapter.
Additionally, the Dark Angels have some meticulously crafted, very entertaining backstory. I never consider that sort of thing expendable. I refuse to even call it "fluff" because that implies that it just isn't important, that I shouldn't care whether I'm running dark angels or a pack of seahorses, as long as my statline is my focus. I never signed on for a statline. The DA won me over hook line and sinker because their backstory struck a chord with me, and I would never want to shortchange the depth of their background for anything. (I do worry about its incarnation in the next codex...)
We deserve our own codex because we're not clones of those other chapters. My deathwing don't operate closely enough to vanilla terminators to be rolled in, and putting in a special sidebar of "if you're dark angels, THIS applies instead" for the DW, the ravenwing, the interrogator chaplains, et all would be wasteful. Why dilute a chapter that has so much character and individual definition like that? I know more Dark Angel players locally than I do for any other chapter, so there's business sense in keeping us apart. That's codex sales right there alone.
As for using the same models, we also have our own. Ravenwing bike squad, Dark Angels veteran sergeants, DA company masters and so on. If we're to say "you use the same models" we could safely ignore every SM codex ever written in favor of one vanilla dex and I doubt you'll find many blood angels or space wolf players willing to sacrifice their dex taht way.
Keep us separate. Just update us, for the Emperor's sake. I find little fault with the current DA dex but yeah, it definitely needs a shot in the arm. We're almost two editions behind now. But keep it separate. Keep the Dark Angels the Dark Angels.