Fast completion with visible cue?

[Simon Josefsson]

Is the following possible with some ad-on package?  If so, would it
make sense to enable the ad-on by default?  If not, what do people
think about adding this feature?

I'm really sorry for the complicated explanation, there is probably a
really simple term for this idea, and I suspect it is already
implemented.  But if so, I'd like to vote for having it on by default.
Many GNOME and GTK programs have similar user experience.

1. CWD is ~.  You wish to open a file
   ~/projects/src/foo/doc/drafts/template/help.txt, so you might press
   C-x C-f ~/proj TAB sr TAB f TAB doc TAB dr TAB tem TAB he TAB RET

2. You edit the file for a while, then close it with C-x C-k.

3. Hours pass and you edit lots of other files, however, consider for
   sake of example that all the files you edit are in ~/play/.

4. You wish to edit the first file again.  You type
   C-x C-f ~/pro

Now, wouldn't it be Really Nice if the minibuffer prompt would
contain:

Find File: ~/pro[CURSOR]ects/src/foo/doc/drafts/template/help.txt

where CURSOR isn't shown verbatim, but indicate where the cursor is,
and the latter part of the string is displayed in a light gray color
but the earlier part of the string is in black.

You could continue typing and TAB complete like the normal prompt, but
would be able to open the "suggested" filename (shown in light gray)
by simply pressing RET.  To really open a file called "~/pro" you
could press SPC DEL or similar.