It's a fascinating question, though largely moot considering the difficulty most people have getting a PC or Mac to take on the role of media server, the cost (or perceived cost) of having a separate PC for that role and general preference of most people to take advantage of some of the features of product that's easy to use, but not invest the time it takes to build something that will do exactly what they want.
It's a great question, partly because it hits on a whole series of migrations in both personal and corporate computing and broadens itself to include not only Microsoft's product strategy and the general direction of technology development, but also just how lazy most people really are.
If I had to bet on whether a PC and an Xbox would be the media (and communication and multi-device storage control) hub for home users, I can't imagine anyone actually taking a bet against the Xbox.
With a PC you have to configure the shares, give everyone in the house rights to both the media and control of connections to the TVs, DVRs, stereos and Slingboxes and a host of other sometimes-aging, always random collection of electronics hanging around the house, which everyone in the house would like to connect the second you mention it might someday be possible.
Even when it should be possible, it's still necessary to map folders on each person's computing, data storage or phones devices to the hub. That has to happen through either cheap wired switches, cheap wireless switches, not cheap but badly designed cable or fiberoptic routers from the ISP, powerline modems from almost anyone, and strings with cans on the end that once connected phones with AT&T printed on the bottom and a warning that the user leased the bakelite, but could not own it.
The Xbox -- despite a tendency to self-destruct, stop working for no clear reason, red-ring itself with no warning at all -- is at least designed to let users network successfully even without knowing anything about networking.
Microsoft tried to solve the home-networking problem before, though to Microsofties the problem is not how difficult home networking can be
Most people are far too lazy to figure out how to make PCs work that way, at least in a way that will continue to work after they turn their backs for even one second. (Lazy, btw, is a geek term describing people who choose the efficient side of a cost/benefit equation when the result shows infinite effort on system integration will result in only moderate and temporary, though notable, success. A geek will pull all-nighters for weeks to make impossible things work for 10 seconds, then break the whole thing down and brag to his/her/its friends for the rest of its life about its technical prowess.)
Barring a sudden influx of people with both good math skills and a poor grasp of what the answers of cost/benefit equations mean, very few consumers are going to use PCs as entertainment hubs, at least compared to the number that buy smart TVs or BlueRay players with Ethernet ports in the back and use NetFlix and online services to act as entertainment hubs.
Even more likely is, in two years or so, when the novelty has worn off the smarphone and everyone has gotten even more tired of searching for the remote, smarphones will become the entertainment hub of the home.
They'll be able to find media by running Google searches of every device in the house, catalog all the media, and present it on your phone screen, which you'll use to choose your movie or music, pointing the ultra-sophisticate smartphone at the TV and pushing imaginary buttons on the touchscreen -- if you even have to look at a screen.
You'll use it as a "remote," probably without realizing it's doing the same job you wished your Microsoft Home Server did in 2007, or that your Xbox did in 2011 or that your cloud services did in 2012.
Maybe someday technology will be smart enough to give you a central place for all your media, you'll sigh, so you'd have something to watch now that American Idol isn't over and Jeopardy is boring that PC wins all the time.
So you'll scan the HD screen of your Android through the entire Canon of Western art, literature, music and performing arts, looking for something entertaining, and not anything worth watching.