I found this list at the emacswiki:
FFI (foreign function interface). Would be great to have this in GNU.
Enhanced Numerics. We sorely need this too.
Apparently much better multimedia support (Of particular interest to me.)
Doubly-linked lists, skip lists, and some other possibly interesting data structures.
Does Emacs have a feature request location, or even somewhere to post issues?
M-x report-emacs-bug
, and viewed at debbugs.gnu.org.