GTK2 has reached its end of life. Correct me if I am wrong, but spotify still uses GTK2. That should be fixed now, almost every other application is GTK3 ready now.
I am also maintaining the spotify package for the archlinux user repository and I am an Arch Linux staff member. If you need any feedback from our side, I am happy to help out 🙂
It does mean, however, that GTK 2 has reached the end of its life. We will do one final 2.x release in the coming days, and we encourage everybody to port their GTK 2 applications to GTK 3 or 4.