I don't see it in a NAS. Over time the helium will leak out and you will end up with a 6TB deathstar, which will fail. It's something I might consider as a data drive in a computer, as long as I have backups on other drives AND I don't mind losing this at some point. I much prefer conventional air filled storage, at least this doesn't rely on exotic gases to run.
As to the preliminary results, apart from capacity it looks to be no better than a standard 7,200rpm hard drive.
Hitachi are great for making advances in technology and getting the jump on everyone else but it usually come at the expense of something. They were first to come out with the 1TB drives, I got a pair of them, Their data transfer was around 70MB/s, had 5 platters and ran hot enough to burn your fingers if you didn't put some kind of forced cooling on them. I think they also came out with the first single platter 1TB drive, while this was another great advance in platter technology, the arm technology wasn't any better so it performed on par if not worse because it had trouble getting onto the correct tracks. I'm wary that they are bring out a 6 platter drive and filling it with helium to try and overcome some of these old problems, I think they're putting in a quick fix so they can claim bragging rights now and sell a ton of drives while a bit down the line we're looking forward to failing drives.