First of all, I apologise for my poor english, as I'm not a native speaker.
Being both a videogame store owner and a lawyer specialized in business law, I completely understand Bioware's stance on this matter. However, in my humble opinion, there are several ways that they can soothe the players agony without having much loss. They can even, perhaps, turn the tide in their favor.
One thing I think they can do, is putting up a poll (like they did with the creation of the default female Shepard), showing up several options of theories for the ending (eg.: the ending being real , the ending being an indoctrination, the ending being an allucination, the ending being a combination of all these theories, etc). They could then commit themselves saying that there will be a DLC following the premise of the winning option (it would be even better if the DLC is for free to avoid speculation).
I, however, understand that most things in business do have a cost. So, if creating a DLC is too pricey for Bioware, they could at least make some kind of written epilogue (like those present in Dragon Age) available for download for free.
Anyway, I have more ideas, but I guess the text would be too long. That's my 2 cents.