The Gnome People are removing the fallback mode because llvmpipe allows graphics cards without 3D acceleration to use Gnome Shell. They have said that they will support a set of extensions that add elements of the classic desktop. Extensions to do this are already available, but they break with each major gnome shell update. These extensions will be updated so that they are compatible with gnome shell at the same time as the release.
I think people are overreacting over the possible effects of this decision. Gnome already provided the fallback mode, which didn't deter projects like Cinnamon, and many extensions are already available to do what these extensions would do. These extensions wouldn't be enabled by default, so gnome is still going for their current interface. Also, these extensions would still be very rigid - they would provide only one different layout, whereas Cinnamon and MATE provide many ways to customize your desktop.
On the subject of switching to KDE/QT, KDE is definitely a good desktop. I've been playing around with the unofficial LMDE KDE, and I am very happy with it. However, KDE still has some problems. First of all, many applications that are very important to users, including Firefox, are GTK apps. While GTK integration in KDE is decent by default, many KDE themes have bad GTK integration. Many good apps are GTK apps, and it could be a problem if they don't integrate well with the theme. Also, KDE is resource intensive - it gives you a lot of eye candy, but it can be very slow on older machines. I give KDE credit, however, for making KDE much faster over time, and for allowing people to turn off effects to get a lighter desktop. I personally haven't experienced this (although I just installed LMDE KDE yesterday night), but I have heard a lot of people saying that KDE can be fairly buggy. Also, in the Mint desktop poll, KDE was behind Cinnamon, MATE, Xfce, and it was just ahead of Gnome Shell, so based on that, Mint users are probably happier with Cinnamon/MATE as the default. Finally, personally, I have never gotten past KDE seeming a little bit too eye-candy-ish. The look and feel of the desktop is a little bit distracting at times for me personally.
On the flip side, KDE has many great features. KWin is as good as compiz IMHO. Also, basically everything can be configured. There are many more good things, but I won't go into too much detail (as my point was to show some of the problems with KDE).
Dell XPS 15 l502x - Debian Testing 64-bit NetInst Xfce, SolydX 64-bit Debian Testing, SolydK 64-bit SolydXK Testing
Old Gateway Pentium 4 Desktop - Arch Linux 64-bit Xfce and SolydX 32-bit Sid