You know what's gonna happen, people are gonna rejoice, then realize that they are pressing the start button to go to the screen to open an app, and then they'll say, "man, this sucks!"
Probably true, but you'll never hear anyone here admit that, at least not for a good long while after its done (if it's done). It's just human nature - we in general don't adapt well. We like to change things to our liking, and will stick to the way we've done things no matter what anyone says. Sometimes it's good, sometimes it's bad. People became very accustomed to the start button and the desktop over the last near 20 years.
Don't know that half-stepping back is going to help MSFT much, but they'll probably try to say that they've at least done something. Problem is that if they don't satisfy critics, then they might end up worse off than if they just let it all sit. Then again, with the regular, yearly, refresh/update of the OS they'll be bale to take another bite at the apple in only twelve months, as opposed to holding off for an entirely new OS in three years or so.
My personal view is that the OS has suffered two problems: a poor PC market to start with, and a lot of bad publicity. The power of the internet is vast. With it being blamed for a continuation of a trend that predated it, and the overall negative push by those who don't like touch integration into their non-mobile devices or the interface since before launch, I know a lot of people who don't want to even give it a try because it just sounds so bad.
Whether you personally like 8 or not, it's relatively obvious at this point that MSFT has to do something to improve reception, because even if there are a good chunk of us who like the OS the way it is, regardless of the reason it's not selling very well. This change they will be able to promote and sell as an improvement, and they hope it will mean increased sales.