> If you have in mind something as radical as pushing Emacs Lisp
> coding towards use of tail recursion.

I don't know what "push Emacs Lisp coding towards use of tail
recursion" means in precise terms, but hopefully Troels Nielsen [1] or
Chris Gray [2] are still working on tail call optimization.

[1] http://lists.gnu.org/archive/html/emacs-devel/2012-09/msg00473.html
[2] http://lists.gnu.org/archive/html/emacs-devel/2012-12/msg00286.html