It's hard to know without it in my hands how big of a deal the stereo camera is going to be. The fact that it wasn't designed for depth (at least publicly stated) makes it a little unnerving - for example having to compensate for two separate focal lengths to get good parallax is going to be a pain. However we built our SLAM around taking on dual cameras IF they happened to show up so we should be ok with some parameter changes on each input.
Don't count on it. Most people aren't interested in AR. And even when you mention it most people will tell you they'd "rather just use it like normal" (ie. no AR)
If you're talking about groundbreaking mixed reality, like the HoloLens or Magic Leap then maybe. Microsoft is doing the right thing by first marketing to business. The consumer tech isn't ready, and won't be for probably 5-10 years (to be at a place where it won't require any overhead.)
Most people don't know what they're interested in and consumers are starting to actually take hold of AR. Ever seen Snapchat filters? Yep those are 3D tracking with depth. Not fiducial AR or just non tracked "overlay" so it counts. It's steps toward HMD AR by showing people what is possible to do to changing the real world dynamically.
Having hardware that can do depth at scale with an application layer is a big step - not sure that the 7 plus gets there but it's a start.
Anyway, AR is about to explode.