Here's my take on all this. Video watching falls into 5 categories for me and just about everyone else I know. 1) Locally stored digitial media, 2) Streaming media from Netflix, Hulu, Amazon, Vudu, iTunes, Youtube etc, 3) DVR'd shows, 4) Live TV and 5) dics.
1) Locally stored digital media. Nothing can beat an HTPC at this IMO. You can get the very highest quality picture out of them and there's a number of very slick UIs to use. That being said, it'll remain a niche product as video libraries for the average consumer will end up in the cloud somewhere and stream to a dedicated device. The minority who don't mind huge HDD arrays and want DRM free are really the market here.
2) HTPCs cannot compete with dedicated streaming devices in either PQ, HD library content or being remote friendly. A Roku, AppleTV, Smart TV or BD player is the best option here.
3) DVR'd shows. If you're willing to deal with Cable Cards, Media Center etc. the HTPCs are pretty good at this. Dedicated DVRs are easier.
4) Nothing beats a cable box for live TV in its simplicity, but if you don't mind cable cards then an HTPC can suffice.
5) BD players are so cheap as to make dealing with the expense, bugs and vagaries of PDVD or TMT kind of pointless.
So, what's really video watching nirvana?
A device that'll support your library DRM free in the cloud, streaming from all the services, On Demand for every current TV show just like you DVR'd it, live TV for news and sports, and disc playback for that odd disc you have. Add a slick, probably voice controlled UI, the ability to run apps
I think the very closest you can get right now is an HTPC for you local "cloud", a good BD player that can double as a streaming device, and a cable co. DVR.
The XBox One can replace the BD player as a good streaming device and disc player, especially if you're a gamer and are willing to use a voice controlled UI. It may be able to replace and HTPC if it has an app that'll playback local files. I have to imagine it will but am not expecting anything too robust. MS (and Apple and Google) all know the market for consumers with extensive local libraries of video on HDD is small and that the future of the mass market is video in the cloud.
The AppleTV has great promise too. I've often looked into the cost effectiveness of ditching cable and just buying the stuff I actually watch on iTunes. However, too much is missing from iTunes and without live TV for sports and news I always quickly give up on the idea. I do expect something new from Apple in this arena in June at WWDC.
If either XBox One or AppleTV can get networks to build apps that'll support both a live TV stream and OnDemand for their shows then you'll really have a winner.
Annecdote: A friend of mine recently bought an AppleTV. They've decided to simplify their lives (got kids) that they''ll just buy everything from iTunes and stream 1080p movies and TV they want to keep from either iCloud or their iMacs.They'll use it for Netflix and Hulu+. They'll use it with their iPads with AirPlay. They'll handbrake their DVD library and put it into iTunes. It's not my idea of ideal but it'll work for them. Oh, and they'll also keep their cable subscription.
I don't see why an XBox One wouldn't do the same for people.