Comment 11 for bug 408651

All additional sequences from GNOME have recently been merges upstream with X.org From now one, please use only the compose key sequences as defined in
  http://cgit.freedesktop.org/xorg/lib/libX11/log/nls/en_US.UTF-8/Compose.pre

Request for changes should be discussed on the X.org development list first before a patch is made since there are more constraints than meets the eye. Most of teh suggestions discussed above have been included already.