Well this will certainly increase the bidding on that specific ad units, elevating the cpc. It is good news for publishers.
What concerns me is the word "fully" in the Google email. The way most sites are designed, it is nearly impossible to have any ad unit "fully" above the fold with the exception of the 728x90 and 468x60 ad units. The skyscrapers don't fit fully in most site designs. Since the 468x60 banner is known for poor performance, it looks like will encourage those 728x90 banners, which most publishers loath. You need to be very creative to get the 300x250 above the fold, blended into content without giving the site the MFA look and increasing the bounce rate that goes with MFA sites.
When myself and many other saw the huge plunge in Adsense revenue way, way back, I did a site redesign that was huge. It was a 100% reorganization of the content, a massive undertaking. I really struggled to come up with something that looked good, didn't look MFA and was visitor friendly. My earnings have skyrocketed, gone three times higher than I have seen for years. I have been able to identify a number of reasons for this massive increase in earnings. There is no doubt the site redesign was one of them. I'm actually in excellent position for this 'above the fold' bidding war.
Having said that, in looking at my current design and all previous designs, that 160x600 banner will never be "fully" above the fold, wont' fit above the fold, no matter what I do. This is unfortunate because that particular ad block is my highest earning even though only two ads in it are above the fold.
I have a small Google custom search box above it, and even if I move the search box, only three ads in the block will be above the fold. The only way to fully view the skyscraper is to push it right to the top of the page, a horrible appearance for site design, not a choice any site owner in their right mind would choose.
While it will certainly push the publisher to rethink their design, in the end, this can only be good news for those who are willing to think outside the box. I know it is going to push me go to back to Ad Planner to check on my ad block descriptions.