Pure speculation in that article, and June seems like an awfully quick refresh rate for the Air. They just launched the new design less than 6 months ago. Historically, they've only updated the Air once a year.
Apple is very tight lipped about their product updates, and out of all the rumors that invariably come out about things, probably at least half of the credible sounding ones end up being way off base.
There are a large number of reasons to take that article with a grain of salt. Not the least of which is no one else seems to have bothered reporting it. There's the fact that the latest refresh launched late last year, and historically the Air gets a single refresh a year. I would honestly be expecting that the iMac would be the next one to get the update. That one hasn't been refreshed since about early July, and would be a far better target for a sandy bridge migration. People don't buy the Air because it's a computing powerhouse. They buy it because it's light, compact, and has great battery life. And for all the bemoaning about it having a Core 2 Duo, virtually every PC netbook has an Atom CPU, which is maybe able to deliver 70% of the performance, clock for clock, of a Core 2 Duo. So while there may be better processors out there, how much sense would they really make for the Air? And if you've ever seen the insides of the new Airs, like I have, there's precious little room for any additional components. The battery takes up probably 80% of the interior, and the bottom case only sits a millimeter or two above the components. The only way you could make room for an additional fan, to get better air circulation for a faster CPU, is to either compromise on the thickness of the system or give up some of the ports. You give up a USB port and the MDP port, you could potentially shift the magsafe port onto the logic board itself, get rid of the I/O board that makes up the left side ports and microphone, and put in an additional fan or just a bigger fan. It's that, or you'd have to get rid of the wedge design and make it more uniformly thick, then you might be able to add either the second USB port or the MDP port back in, but probably not both unless you wanted to remove one of the speakers. Seriously, there is NO wasted space inside the Airs, so any additional heat given off by the sandy bridge CPU would have to be offset somehow, and I don't see how they'd do that as things are now.