It's not really surprising the MBA's have been ready for awhile. Even before TB was on the MBP's, Apple was testing the port on prototypes of all of their models. The SB processors will finally be used because the IGP HD 3000's are finally somewhat comparable to the outgoing Nvidia 320m's. They didn't put the first gen i7's in because the IGP was MUCH worse than the 320m's, and would have been too much of a negative impact on the MBA's overall performance to justify the processor upgrade.
I wish they would send them out now, since the upgrade to Lion would be free, but Apple wants to maximize the install base of Lion so they can brag about the numbers to the shareholders. It makes sense, but yes, I want my MBA now.
Also, the only thing left to wonder IMO is whether or not 4GB RAM will be standard and 8GB available, backlit being brought back, or whether or not Apple will use ULV or just LV processors. While the Core2Duo machines have a separate CPU (17w) and GPU (10w), the SB have the CPU and GPU made together, so when they're talking about power consumption, it includes both. This means Apple could use LV processors instead of ULV, because the LV's are 25W, and the ULV are 17W. The current thermal design allowed for 27W, so 17W is way below that. I think they'll probably use the ULV on the 11" for battery life improvement, but I hope the 13" will use the LV processors.
Oh look everyone we have an Apple employee in our presence. He CLEARLY knows everything

I was just offering my views about alls that is going to be updated and I don't think Thunderbolt will be added. They barely offer enough ports on the MBA as it is. As port space is very important on the MBA I really don't think they will until it has taken off properly.
The point of the TB port isn't just that it's an amazing port to connect SSD externals too. The point is also that with it's 10Gb/s throughput, you can connect a hub to it that will connect to multiple USB3.0's, eSata, Displayport, etc., without sacrificing ANY of the max throughput's of any of those ports. You can also daisy link devices.
It actually makes MORE sense to put it on a port-limited computer because it allows to connect a ton of devices through one port.
Besides, Apple has a 1-year exclusivity agreement on TB. They want it on every computer to maximize its presence in the market before PC's get access to the devices so they can use it as a selling point for Macs.