I believe a fork of KDE 4 is not only a bad choice and almost impossible. It's also silly. Because the basis of KDE4 gives you so much freedom to customize everything on the desktop that it would be much easier and more sensible to simply recreate a KDE3 look&feel for KDE4.
Now let's see if the people bringing the complaints will deliver this or just keep shouting and complaining about it.
Look at the well written plasma libraries and you will know what I mean. KDE4 is a huge step and it's just amazing I could install the great vocabulary trainer parley unter windows with just a few clicks. This means you write your application with the comfort of KDE4 but you can use it under Windows, OS X, Linux and possibly other operating systems.
Check out this groklaw article for more.