I have a hard time envisioning a wear-everywhere headset any time in the next 5 years that passes as a normal pair of (sun)glasses at first glance, is useful enough to be worn all day, has enough battery life for all day usage, and has decent visuals.My guess is that there will be two versions. A bulkier VR headset for home use, and a more lightweight pair of AR glasses (which I imagine will be almost identical to a normal pair of spectacles) that you can wear outdoors all day just by tethering to your phone.
With Apple, the best way to approach this is to imagine what sort of experiences a product can enable. Live sports and concerts would be an interesting way to start.
You could have something like Siri glasses, where the primary interface is audio. Maybe you could even have a tiny visual HUD. But that's not really AR—at best it's just the Apple Watch in a different form factor.
I don't think there's a lot of overlap between phone/tablet AR and head mounted AR. From a technology standpoint it's similar—Apple's work on ARKit is certainly going to pay off for head mounted AR. But for actual use cases, I don't see much overlap. If AR were useful in a phone/tablet form factor, it would have already gotten a lot more use. I'm a bit of an enthusiast in the VR space, and have tried several iPad AR apps, and while it the technology is impressive, I haven't found much of a use for it. On the other hand, I've spent hundreds of hours in VR social, gaming, and creative apps. If visual quality is significantly improved, I could see myself using VR even for mundane computing tasks.There probably will not be a huge gap between this headset's AR mode and the AR mode on a iPhone. The immersive impact/effect would be different but pretty good chance would not have to completely rewrite the app from scratch.
There is a two fold scale impact there. First, a limited subset of developers could do AR app development on iPhones ( like already doing for last couple of years). Second, some AR headset app developers have an outlet beyond the headset for the slightly different app build for iPhones/iPads.