Hou about this start with?

This might be a kind of talking about usability, although
RMS said in mail it seems not good idea to him.

The folowing is an experimental implementation of readline-
like interface in shell buffer.

;------------------------------------------------------------------------

;;;;
;;;; C-z (in any buffer) pops up shell buffer.
;;;; C-p, C-n, C-a and C-l, work just like readline in a prompt line.
;;;; C-x f goes to fundamental-mode and C-z restores it again.
;;;;

(require 'shell)

(global-set-key "\C-z" '(lambda ()
                          (interactive)
                          (shell)
                          (shell-mode)
                          (end-of-buffer)))

(add-hook 'shell-mode-hook
          '(lambda ()
             (define-key shell-mode-map "\C-xf"    'fundamental-mode)
             (define-key shell-mode-map "\C-i"     'comint-dynamic-complete)
             (define-key shell-mode-map "\C-a"     'comint-bol)
             (define-key shell-mode-map "\C-p"
               '(lambda (n)
                  (interactive "p")
                  (comint-previous-input n)))

             (define-key shell-mode-map "\C-n"
               '(lambda (n)
                  (interactive "p")
                  (comint-next-input n)))

             (define-key shell-mode-map "\C-l"
               '(lambda ()
                  (interactive)
                  (recenter 0)))))

;------------------------------------------------------------------------