Here's another way to illuminate the distinction between content-based and brute modality. The former is merely a matter of identifying alternatives ways for worlds to be. The latter is concerned with whether those ways really had a chance to be actualized.
Imagine yourself wanting to buy a Ford back in the days when you could have "any colour you want, so long as it's black." All the cars are black. But blue cars were still possible, in the sense that a car's being blue is an alternative to its being black. (On this understanding, "possible alternative" is redundant. Possibilities just are alternatives to the way things are.) But it's not an alternative you, as a car-buyer, have access to. It's not an option you can take. So a blue car is not a possibility in this more involved sense.
Of course, that latter sense is a lot narrower than metaphysical possibility, even of the brute sort that I have in mind. The analogy is imperfect. But I hope it is at least suggestive. We can imagine other world-states that are alternatives to this one. That gives us the standard space of possible worlds. But it's a separate question whether they're possibilities that "could have been taken" (by God, or the cosmos, or whatever). We can still ask whether they are really possible, in this more demanding sense.
The question can be reworded using the lump/property picture described in my previous post (but ignore the essentialism stuff). Each alternative is a property. But, we may think, that by itself is a merely ontological fact: these abstract states exist. One of them is actually instantiated by the world-lump. But what is the modal status of the other world-properties? They're alternative properties to the one that's actually instantiated, but are they ones that "could have been taken", that really could have been instantiated by the lump? (It probably isn't fair to make the word "really" do so much work here. Unfortunately, I can't think of any better alternatives...)
1) Am I making any sense here? Are there any clearer ways to get at this "brute modal" notion?
2) Is the notion itself fully coherent?
3) Does it correspond to reality? (Is this brute modal status held by some events but not others, say?)
4) Can we establish either way whether all possible worlds are "really possible" in this sense?
5) Are there any other questions I should be asking here?