I suspect that HDMI passthrough will be a frustratingly unfulfilled promise, as it is with Google TV.
Recent GPUs are virtualizeable (using multiple command queues); this is mostly targeted for VDI or cloud gaming but unused in PCs. http://www.nvidia.com/object/enterprise-virtualization.html
There are tons of edge cases you run into when you don't have full control of the tuning stack. As one example (I can think of dozens easily):
Family has a single-tuner old school Scientific Atlanta DVR (still very popular with cable operators despite being horribly obsolete). They set it up to record a show, it is currently recording said show, person interacting with the Xbox One does something to change the channel to one different than the one being recorded on... oops! There is no way for the Xbox One to know this is a potentially destructive operation for the DVR. At worst the DVR changes the channel and loses half your show, at best the DVR is smart enough to prompt you about this and stop the channel change, but how does the Xbox One know this occurred? There are some high-end DVRs with APIs that exist in an attempt to deal with situations like this but they are very few, very far between and there are no standards for them.
Corner cases like this present themselves all the time with these HDMI-in/HDMI-out devices like Google TV and they are inherent problems with the current state of set-top box technology. No matter how many resources Microsoft throws at this, the end result will still be kind of lame a lot of the time and a far cry from the seamless experience you see in the on-stage demos.
What if this wasn't classified as a corner case? As you said - most MSOs are running either an old Moto or old SA as their standard box. Because headends are either Moto or SA there are actually very few unique STBs in the field. And of those, they are all versions of the same OS that either Moto or SA have been using for a long time.
If MS just threw a bunch of resources at common SA and Moto boxes to enumerate and add special code to handle these cases... could it work? Would it be a better experience? Is it worth it?
Unless, of course, the pass through works when the device is turned off... However, I haven't heard any mention yet that it does (does anyone know if it will support this?).
And plus, if you had any other multimedia devices (e.g. a Blu-ray player), wouldn't you still need to use the other inputs on the television anyways?
Microsoft's betting the farm on the idea that a consumer will leave the xbox on 24/7 in a low-power state and have it as THE hub for all things digital entertainment. Your TV goes through it for advanced features such as TV channel guides, extra content, etc. You play games on it. You chat, take video calls and the like on it via Skype. You steam music/movies to it as your media player. All of it is controlled via the Kinect gestures and voice recognition. It is also why they're planning to push updates/etc. through in idle times (e.g.: overnight) when the device is left in low power but able to do basic tasks.
Basically, MS wants to take the beachhead they established with the first two generations and expand it. They want the Xbox One to go against the Apple TV and XBMC media centres and the like to become the all-encompassing portal of your entertainment.
Sure the hardware will be similar, but what use is that if the APIs to access the hardware are totally different? I think the odds of Sony using DirectX in their SDK are pretty slim.
The hard part of the previous generations multi-platform had been in getting to the same level of performance. E.g. 360 had a pretty weak CPU and a superior GPU compared to PS3 so the distribution of things done on CPU and GPU was completely different between these two targets.
- PS4 and XBox One are going to be similar hardware wise, with the PS4 having an edge in raw power and the XBox One having an edge in "cleverness" (e.g. memory caching) and power consumption (lower).
- Microsoft is re-using Hyper-V in a very awesome way(!).
- HDMI passthrough is Microsoft's "ace in the hole."
- Developers are going to have a great time this generation thanks to how similar the hardware is (identical in many cases).
I really want to know how Microsoft is able to run two hypervisors and offer GPU acceleration to both concurrently. Is this part of AMD's new CPU+GPU on one die magic, or is this something we'll see on the PC?