I think that the whole notion of "it's nice to know I could upgrade" is primarily a consequence of what's currently in the system. Consider the next upgrade.
You buy this thing in 2013. For bulk storage, you hook up a usb 3.0 raid array and a cheap usb dvd drive. A couple years later, you decide you need more fast storage, so you add on a 512GB / 4 TB thunderbolt fusion drive box (note: this product doesn't exist today). Next year, you upgrade the USB raid array to thunderbolt and decide you want an external cinema quality 4k / THX video converter, that also connects over thunderbolt.
Then in 2016, you conclude that the 24 core macbook pro is sufficient for your day to day, and hook up your bulk storage to that when you're home, but leave the cinema converter and the old usb raid array hooked up as your htpc.
Incidentally, to address your specific scenario, I'm pretty sure that an Apple TV costs less than your gt120 did.
In other words, you doubled down on the tail end of one way of doing things, and little of that will carry over to the new standards. It's the same situation many people were in with AGP graphics cards, IDE hard drives and ATX power supplies without the additional 12v connector.
I definitely see what you are saying, and that is why I do think it is a very impressive and very cool computer.
But a lot of the value for me was the one device. A single, unix based[1] device that did everything from be my htpc to be my fileserver to be my desktop, music player, build box, run all my vms, etc.
I derived a lot of value from that. Even if the second device is an apple TV, it's still a second device.
Also, diverging a bit, a lot of folks are talking about a lot of video based expandability via the thunderbolt ports, but remember - it's not even as fast as 4x pcie ... 10mb/s over copper vs. 120 mb/s ... if I have my numbers right.
PCIe 4.0 is double the bandwidth of PCIe 3.0, which is about 1 GB/s per lane, or 16 GB/s for PCIe 3.0 x16. PCIe 4.0 x4 would be ~8 GB/s, and x16 would be 32 GB/s. Unfortunately, the spec won't be finalized for another couple years.
I feel like Apple is betting the farm on Thunderbolt being the future, and I don't see that future materializing. How many Thunderbolt peripherals have y'all even seen in real life that weren't the Apple external monitor or a mini displayport display adapter? I feel like this is even less prevalent than Firewire was back in the 1394 glory days (it was/still is an excellent bus for running audio, due in no small part to the fact that it's not USB; separate controller, doesn't crash if your USB bus gets wonky, etc.).
They're not "betting the farm" on it: they're locked into Thunderbolt because Intel sold them an end-to-end platform, from CPU to chipset to everything in between. That "everything in between" includes Thunderbolt; it's the reason you haven't seen the latest USB on a Mac in forever. Even in spite of a dearth of options, Thunderbolt was the only way to go on a Mac because Intel said so.
"it's the reason you haven't seen the latest USB on a Mac in forever."
Do I misunderstand what you mean by this? USB3 is rolling out on Macs and available on most of them today. (I think the Mac Pro is the only one currently lacking it.)
Right, you can get it on the very latest Macs, most of which are just rolling out now and none of which have been out for more than a year. USB 3 is old at this point; most manufacturers started shipping devices and computers with USB 3 ports in 2009. But because Intel didn't adopt USB3 until their Panther Point reference platform in 2012, Apple really didn't have much of a choice.
(Intel really, really wanted people to use Thunderbolt, even though there weren't any Thunderbolt devices available.)
It took four years from when the standard was finalized for Macs to finally start shipping with USB 3.
Oh wow, yeah... didn't realize it was 20 Gbits/s for TB2 and not GB. It's not even close to as fast as currently shipping PCIe 3.0 x16, at 2.5 GB/s versus PCIe's 16. I guess external video cards are not really much of an option. Even using up all six TB2 ports won't get you as much bandwidth as a single PCIe 3.0 x16 slot.
Thunderbolt 2 is 20gbps = 2500MB/s. Raw 4K video maxes out at 776MB/s, RED has compression that pushes it down to 2.5MB/s. The Mac Pro has six ports, so a total of 120Gbps (15GB/s), if the controller can handle that.
You buy this thing in 2013. For bulk storage, you hook up a usb 3.0 raid array and a cheap usb dvd drive. A couple years later, you decide you need more fast storage, so you add on a 512GB / 4 TB thunderbolt fusion drive box (note: this product doesn't exist today). Next year, you upgrade the USB raid array to thunderbolt and decide you want an external cinema quality 4k / THX video converter, that also connects over thunderbolt.
Then in 2016, you conclude that the 24 core macbook pro is sufficient for your day to day, and hook up your bulk storage to that when you're home, but leave the cinema converter and the old usb raid array hooked up as your htpc.
Incidentally, to address your specific scenario, I'm pretty sure that an Apple TV costs less than your gt120 did.
In other words, you doubled down on the tail end of one way of doing things, and little of that will carry over to the new standards. It's the same situation many people were in with AGP graphics cards, IDE hard drives and ATX power supplies without the additional 12v connector.