Yes, they could have done the same thing with an Android WebView. But the Chrome team is actively working on implementing WebVR (which also want to support many AR use cases) so they already have a native (= higher performance, lower latency, etc) implementation to modify with some smaller changes to use the ARCore API.
There's actually a couple of Chromium-based browsers on there, Samsung Internet for GearVR which has been out and quite popular for 360 video watching (Youtube.. etc.), and Oculus just came out with theirs.
Yes ideally they'd be able to be composited together at the depth buffer level. But even separate I can see a ton of devs making some very cool more UI-centric applications just with CSS mode. Can't wait to see the webdev community understand what can be done with VR and the webstack in 2016.
Really looking forward to the the stereo rendering of non-WebGL content, HTML+CSS, which the Mozilla team is working on. More challenging path to figuring out but will open a lot of possibilities.
On the Gear VR (dev kit, 2014) there was a 2.5k screen at a smooth 60fps. The consumer Gear VR coming out this fall will likely have a 2.5k screen but we'll likely see 4k screens on mobile headsets in 2016. 120fps will be a nice improvement but not required, with the Rift CV1 at 90fps and sufficient for presence. So we're talking a 2-4x difference.
The graphics card issue is not that relevant, Gear VR with a mobile GPU is showing that it's not really about some arbitrary graphical fidelity bar. Yes, some of the highest fidelity cool stuff will be on PC but multiple cards won't be required. Both the Vive and CV1 will run great on one high end card, and by the time they upgrade to ~4k/120Hz... they'll still require just 1 card.
I don't disagree completely but underlying the growing excitement was for the past 18 months (since Abrash, etc. started talking about VR and presence as something incredible, game-changing and deliverable in around 2 years) was in large part based on the pace things were advancing and what was in store for a consumer release.
Plus many of his specific points are just so temporary in nature, like resolution complaints, heaviness/comfort, tethered, form factor, etc. These will be solved in just the next few years.
It's parts of your lower brain aligning to convince you you're in a virtual world, and while it is a spectrum you really need a high end headset to experience it. Abrash himself mainly dismissed VR's potential prior to experiencing it.
Jeff is speaking from a position of not having tried the good stuff that delivers a sense of 'presence' in the virtual world. That is the game changer, the thing that is making people believe something special is on the way. When he says "I have experienced modern VR. A lot. I've tried both the Oculus DK1, the Oculus DK2." he's just flatly wrong, he hasn't. Those headsets at not modern VR and using them as the reference for where VR is at is pretty crazy.
But you'll get a chance to try to presence-inducing stuff in the next ~6 months with the consumer release of the Vive and Oculus CV1.