Yesterday, Steam had staging area for the Valve Index VR headset pop up with some interesting information. Some folks captured the image before it was taken down, but Valve's PR head Doug Lombardi confirmed with The Verge that it was indeed a legit posting and some additional information.
May 1st is when they'll be taking pre-orders with a release date hopefully in June, although that can change. The Knuckles controller is now called the Valve Index Controller (although they missed an opportunity to keep the controllers that and call the HMD the Knucklehead, but that's ok.) and they will come bundled with the headset.
The page had some additional information such as being tethered via a DisplayPort cable and a USB cable and also comes with a power adapter. Two face gaskets will also be included as well. The listing might not have all that it comes with though, but Valve did confirm the information was accurate.
There was a rumor that Valve would also sell the HMD by itself without the controllers or lighthouses since it is backwards compatible with the Vive accessories in case someone wants to save some money, but we won't know that for sure until they officially announce the Index.
Another rumor is the displays on the Index will support a resolution of 2160x2432. JDI LCD panels to be exact. That would be pretty exciting if it indeed is true.
I'm guessing we'll get all the information on the headset on May 1st, but as always leaks can happen and plans for an official unveiling can change. I will say these are pretty exciting times for VR enthusiasts and the Valve Index looks really promising for us waiting on a next generation VR headset to play with.