Meanwhile, it might help: I just installed GIMP 2.8 from a working PPA (64bit).
sudo add-apt-repository ppa:otto-kesselgulasch/gimp (not sure, you might also need [otto's ppa]/gimp-libs) sudo apt-get update sudo apt-get install gimp
I run 2.8 now and it's great!
Meanwhile, it might help: I just installed GIMP 2.8 from a working PPA (64bit).
sudo add-apt-repository ppa:otto- kesselgulasch/ gimp (not sure, you might also need [otto's ppa]/gimp-libs)
sudo apt-get update
sudo apt-get install gimp
I run 2.8 now and it's great!