preexec hook: possible enhancement?

[Matthew Wozniski <godlygeek@xxxxxxxxx>]

While we're on the topic of using the preexec hook to set the
titlebar, I'd like to bounce something off the list and see if 1) it's
possible and 2) people would consider it useful.  So, would it be
possible and/or useful to have the preexec hook (or some other, new
hook) fire once for each pipeline in the current command, rather
than just once using the entire current line?

For instance, if one were to type
% xterm ; echo google.com | xargs w3m ; gnome-terminal
could a hook be inserted to fire once with "xterm", once with "echo 
google.com | xargs w3m", and once with "gnome-terminal" passed to it,
rather than just once with
"xterm ; echo google.com | xargs w3m ; gnome-terminal" passed to it?

It's by no means a necessary feature, and I don't know if others would
even find it useful, but I think it would be pretty cool to watch the
titlebar change as we moved from one pipeline to the next.

~Matt