Once again, you're talking to yourself, making us guess what you mean.
> The effort you depose to write tabs for emacs can be compared with
> the effort to add to emacs a real graphical interface
here is a video to see what I am talking.
In this video you can imagine that the workspace is a frame or buffer or window of emacs.
I can write a minimal smalltalk system in less than 4000 lines of code , and it supports minimal graphics.
Emacs does not have millions of lines of code as you say : just run a command like 'cat *.c *.h | wc ' in ./src to convince yourself.
No lisp line of code needs be changes, and all functionality would maintain as now.
Once you have the tendency to say that you use widgets , you have the tendency to use graphics, so you need a graphical interface.
I bow out of this thread definitively now.