As a MacPro owner, I do see a requirement for Thunderbolt - personally I'd prefer to own a single set of peripherals which I can use for both my desktop and laptop.
This is the biggest reason to do so (TB on a desktop with slots). But keep in mind, this is a niche market within a niche in terms of the MP.
It has a larger audience IMO though, as other systems open up the consumer desktops with slots to sharing peripherals with laptops as well.
There's also another small note, but potentially of increasing importance over time, is the fact some product development will center around TB ports. Think video cameras (not just professional models) and cell phones for example (
HTC ThunderBolt 4G Android is already on the market).
If there's no way to get a TB port in an existing desktop equipped with slots, then it could reduce the sales volume of such products, as I don't see consumers rushing out universally to replace their machines just to get a TB port in their machines.
Intel has stated that there will not be any PCIe/Thunderbolt expansion cards, but it's not clear whether there are technical reasons for this, or whether it's a marketing move.
I've seen it both ways (statement of NO was during the live feed by one person). Yet others stated it in a manner that contradicted this, and none of the official documentation on Intel's site states "No PCIe cards will be available".
Given the devices that are being designed around a TB port, not allowing a PCIe implementation would be a bad move for those vendors, and in turn, they'll pressure Intel to allow it at some point. Which I think is the key (happen later on).
The reason I suspect for the confusion, is to improve adoption rates. Imagine a simultaneous release of versions that do Data + Graphics signals and Data Only. It would be a mess (angry consumers that purchased Data Only solutions trying to run a monitor).
So by waiting, it helps adoption. It also buys them time to settle on a standard to implement a PCIe card, particularly if it's to obtain DP data off of the graphics card (interconnect specification between a TB card and GPU card). An alternative solution = place the TB chip on the graphics card itself (PCB surface area and cost issues that make the interconnect implementation between separate cards more practical IMO).
Intel haven't yet published detailed public specs for Thunderbolt - as far as I'm aware no one has yet independently verified the feasibility of implementing it on an expansion card for older computers.
It would be impossible for existing AIO's (no slots of any kind) that don't have a TB chip installed to get one.
But for systems with slots, it's technically possible at least for a Data Only implementation (it's just a PCIe 4x lane connection at this point, as the DP input pins will remain unconnected).
They specifically state that it's the price of the host controller, not modulator or device controller (although it is possible that their source have mixed them up or something was lost during the translation (most likely an Asian source)).
