Firstly, I think this rumor is false. But if it turns out to be true, is a non-issue. I don't see why they wouldn't be able to reduce the amount of ram used by the OS. I think the xbox one will do the same for its OS also. It's to be expected.
I remember an old rumor from march: The ps4 was supposed to have 4gb or ram with 500mb used for the OS. I'm guessing since most games won't need more than 4gb of ram at launch - they decided to use the extra ram to make the OS as smooth as possible while working to optimize it.
Either way, if Battlefield 3 is only using 4 gb of ram (At the most) and is running at 60 fps. I think we're doing fine.