I own an Xbox 360, a Wii, I owned a Wii U (but was so underwhelmed I brought it back).
I've had several consoles over the years, but I keep going back to PC gaming. My 360 collects dust - it's not worth paying the online tax to even watch netflix on it. The Wii is used for Wii Fit only. My 4 year old son prefers the games on the computer. I don't know why - he just does - with one caveat - they work with a controller.
I was looking at possibly the XBone for the living room - but it won't play 360 titles - and the entry price is very high considering I'd have to restock the titles at ~$60 a pop.
Now that Steam has announced SteamOS, Steam Machines and the Controller - I can kill many birds with one stone. I can buy a modern console for the living room. I can keep my current library of titles (that I've been building since 2006). My son can have a controller that's the same for both devices. I can stream old games, hopefully though there will be enough native releases - because that will be a key point to most people. Now that Steam will offer Family Sharing/Controls, I can finally stop buying for 2 accounts and just focus on building one library. For myself, this is a great solution.
Now, will people who exclusive use PS/Xbox switch? I don't think so easily. First, you have the Madden crowd - good luck getting EA to budge on releasing sports games for the PC again. Then there are the exclusives and the kinect. I know Kinect is a failure to a lot - but it is a great family device and one of the only things I fire the Xbox up for all anymore is stuff like Sesame Kinect...
But - as these machines proliferate - I can see more and more people picking them up. This is pure speculation - but I imagine they will refresh the hardware frequently - like phones and tablets. Being and Open System - I can see many of it's own exclusives - whether whole titles or features in a title. The idea of being able to self-upgrade is phenomenal. I imagine over time these machines will become more than just different form factor PC's - and may offer some sorely needed innovation in the market... SteamOS makes that possible - kind of like an Android for Consoles - just even more open.
The worse case scenario is it doesn't pan out great, and not a lot of manufacturers fizzle out on the idea and SteamOS/Machines become a footnote - but the damage is already done - because a game optimized kernel will exist with opitmized graphics drivers - something sorely lacking for Linux for many years... So even a short term failure could lead to greater things down the road.