I want to upgrade Bluetooth Card(Airport Card).

Correct! The MacBook Air mid '11 has BlueTooth 4 LE. Its just turned off! The tool is all thats needed to enable it. Why Apple disabled it in Yosemite is a mystery.

@Dan, I guess Apple wanted people to upgrade. The tool is awesome...I have done this on two machines the longer manual way and upgrading airport card, wish I had that tool before. I would have definitely made things a lot quicker.

I think the issue is more complex than that. Apple still only has a finite number of testers in-house for the OS release. As these OS's get more complex they are often put into a time squeeze and have to limit the testing to key systems as there is no way they could test every Mac with all of the configurations it could have. Then when a hardware upgrade is needed to support a new feature that really throws a monkey wrench into the mix now they need to do both the unchanged system and then the upgraded model. OK, now look at the software coders perspective how do I create the line in the sand: I think that is why some models that do have the right BT board got cut off. Maybe Apple will get the hint here and come out with a updated version of Yosemite for upgraded systems. And, maybe Apple will give guidance on what it expects for BT hardware per the different series (the ones that can be upgraded) so people can either do it them selves or get it done.

In any case the chatter of people wanting Handoff/Continuity is growing. I'm sure someone in Apple is thinking how do we address this: are we going to be be corporate stiffs or community hero's?

Business is business. The compatibility thing isn't a testing or beta issue...Apple has millions of registered "devs" with machines that vary in specs. Apple knows this is going to be a highly regarded/wanted feature and use that to their advantage. It's pretty clever if u think about it. I have done this on my personal machine and everything works flawlessly. I have a SSD, 8GB of RAM, pretty decent CPU, my machine is snappy and has never given me any issues. I would not have upgraded anytime soon. I'm pretty sure there are plenty of people who feel the same. The fact that certain machines are capable of supporting these features on the hardware side, but were blocked off by code was done because the Pro models of that same year did not have the same Airport Card, and I'm pretty sure Apple knew they would have a problem on their hands when people started asking why the Airs and Minis had BL4 and the Pros of that same year did not have BL4.