Sony anounced Project Morpheus - their VR headset - to be launched in 2016. They did showcase working models with demos, one of them was a Sword Art Online demo, so SAO is pretty close, actually.
There are various mmos with VR support on the way (ryzom and The Rift are already playable, and a bunch of titles under development), and the technology is mostly available for the hardware, mostly the hardware itself as well.
Virtuix Omni (http://www.virtuix.com/)
Novint Xio (http://www.novint.com/index.php/novintxio)
ControlVR (https://www.kickstarter.com/projects/controlvr/control-vr-motion-capture-for-vr-animation-and-mor)
P5 gloves (http://www.cwonline.com/store/view_product.asp?Product=1179)
Razer Hydra (http://en.wikipedia.org/wiki/Razer_Hydra)
The Hug Shirt
(http://cutecircuit.com/collections/the-hug-shirt/)
So in all, 2020 is more realistic for a VRMMO knowing all the hardware is close to ready.
Not talking about perfect but at least a working VRMMO.
The problem is NOT the fact that people need a VR headset, even the Oculus DK2 is good enough for a playable and enjoyable VRMMO, and it's 350$ price isn't too bad either.
The problem is that the PC powerful enough to give a good experience with, ended up costing around 4000$ which is not an amount an average gamer would want to spend.
As for the totally immersive version as seen in SAO: it's pointless, then you would have to actually run inside the game for hours and you would get actually tired. I certainly wouldn't want that. It's a lot easier to sit in an armchair pushing buttons.
So in short:
According to Sony, VR is coming in 2016.
http://en.wikipedia.org/wiki/Project_Morpheus_%28virtual_reality%29
There is a fully working space shooter VR mmo already available too.
http://www.elitedangerous.com/