The problem I see with that is it just turns the issue around. Because I believe ALL the elect already have what is promised, just as Mary does — again meaning that Mary is not currently “special”, or in possession of something regarding salvation and sinlessness that the other Elect do not have.
I would however further agree that, being dead, Mary has a state different from the living Elect. Her state is the same as the other Dead Elect.
Having said THAT, I will further state that knowing what is true in the living world is hard enough without knowing what is true of those who have died. So long as nobody asks me to take personal action based on their belief, you can pretty much believe whatever you want about what happened to Mary when she died, or what happens to the rest of us. It doesn’t effect me now, and when I die I’ll find out what is next.
The rest of the specialness would be another argument. But I think the first thing to settle is that we don't think she has anyting that she did not receive.