new-tabs doesn't do the favicon or the close button, but with css you can get
active-tab and name-shortening.  it does have buffer-number.  perhaps the tab
format could be user-configured somehow to accomodate favicons and close
buttons.

I put a note about styling new-tabs at http://conkeror.org/StylingChrome

It could use some minimal default css.  (though register_user_stylesheet would
not be the right way to provide such default style, because cascading order is not
guaranteed with that method)