Hi guys,
I've actually registered in this forum just to post this reply, as I've been absolutely enraged by Apple for changing this feature. Like steve-p said, there's no sense in changing an established cross-plattform standard. In addition, the new cmd+[ shortcut is especially painful for international users such as myself who don't use an english keyboard layout (I actually need to two hands for this shortcut on a german keyboard).
tldr: I did some poking around and found a way to restore the old backspace shortcut. Here's how:
1.) Set an arbitrary shortcut for the command in the System Preferences
2.) Go to ~/Library/Preferences and open the com.apple.Safari.plist file
3.) Find the NSUserKeyEquivalents key.
4.) Replace the shortcut you had previously set by this one: "⌫"
5.) Profit!
Any questions: hit me up on twitter - @jrigerl
Wow that would be fantastic to get it back. Unfortunately I don't have "NSUserKeyEquivalents" located anywhere in that file. Ideas? Am opening the PLIST wrong?