Having only a laptop.
With an external GPU you can get best of both worlds: an ultrabook that you can have with you at all times and the performances of a heavy rig when you want to play.
With your micro/miniITX you’d have to buy 2 computers with one being used only for gaming.
I didn’t even know that this type of thing even existed. It is a little high for my liking, but I will have to check out some thunderbolt GPUs for my crusty HP laptop!
There’s a company called EXP that makes a device called the “GDC beast” that breaks out expresscard, mini PCIe or M.2 slot into a fairly small, externally powered dock. I’m kinda hoping for a tbolt 3 version since those things are pretty cheap (50-70 usd) compared to most of these, but not hot swappable or as flexible as most of these other options. That would probably put this in the price range most people wouldn’t feel too terrible about.
Razer’s hardware is sweet, but at that price + a decent mainstream video card, I might as well get a desktop and stream things over.
I totally forgot about this post but the new one that went up today had a link to it – funny timing, as I just read this article yesterday. You can spend that much on just one 1070 if you really want to, though the pricier cards might perform better. Still, might be a good sign of a real market emerging.
I actually picked up the Blade Stealth + Core bundle at the end of last year when the Intel 7th gen Blade Stealth came out to replace my aging i5 2500K desktop and my cheapo commodity laptop and it’s been phenomenal. If you buy the bundle Razer knocks $100 off the price of the core, so it’s still pricey, but a little more manageable. I have an older GTX 980 in it that works like a champ when I’m at my gaming station, but I can disconnect it and have a nice light and portable laptop to take with me anywhere without feeling burdened down by the likes of a “gaming” laptop. It has some occasional hiccups, but overall the system is very stable and fills my needs perfectly. Plus what’s better than having one main computer for everything!?
I can understand why this would be desirable on laptops, and other AiO devices - but isn’t the GPU upgrade cycle already decoupled from the system upgrade cycle on PC?
I see this more as an interesting option for gamers who prefer laptops, over desktops.
Even integrated graphics are becoming quite capable at 1080p these days, so it’s really only of interest as 4k becomes more mainstream, or those with high refresh rate devices, at which point your bandwidth requirements start going way up.
Unfortunately, I don’t really see thunderbolt as a future-proof solution to these problems just yet. Once you compare the bandwidth of PCIe, the bandwidth of DisplayPort, and the bandwidth of thunderbolt itself; and just what displays these things can drive; you start to see that we’re already approaching limits of the tech - and new cables/standards are needed to drive the high-bandwidth displays that would drive you to consider these devices in the first place.
I very much think there’s a small niche for them to cut out with current-tech, and it appears that you are in it! So congratulations on your purchase, and I hope you and your son enjoy many hours of gaming fun 
I am not sure that applies; the display (except in loopback laptop mode) is driven directly by the video card so the bandwidth is all compressed data being sent to the video card – h.264 and h.265 video, 3D textures and 3D geometry, etc.
I must say that this new thing is extremely cool and useful for some people. I really hope these units will become more common and be future developed. 
The GPU of the Skull Canyon NUC (Iris Pro Graphics 580) is not nearly as fast as the GPU of the PS4.
The Iris Pro Graphics 580 has 72 cores with 1000 MHz.
The PS4 has a GPU with 1152 cores with 800 MHz.
According to these specs, the PS4 is over 12 times faster than the Skull Canyon NUC. Although for some reason the Iris Pro Graphics 580 is able to get way more Gflops than it should have with its really low 72 cores.
The Skull Canyon NUC has 1152 Gflops.
The PS4 has 1840 Gflops.
The PS4 is 60% faster than the Skull Canyon NUC and it’s cheaper. Even the Xbox One (1.31 Gflops) is faster than the Skull Canyon NUC, although only by 14%.
Whatever math you are doing here, it has little to do with real world performance. Compare the battlefield 4 framerates. Same game running on both platforms.
And
Note that 1280x720 medium details, which is what the PS4 runs battlefield 4 at, is well below what the skull canyon was tested with
Dropping the resolution down to 1366×768 and setting the graphics to high details improved the FPS to 41/49.64/64 and dropping the details even further down to medium increased the frame-rate to 48/58.42/73.