multi-lined header-line?

[Peter Mao]

Is there any way to configure the header-line so that its text will
wrap, making the header more than one line tall?

I wrote a minor mode (arxiv-mode in the emacswiki) that lists
subdirectories of the current directory on the header line, but
sometimes there are too many subdirs and the scroll off the page.

If this is not currently possible, how does one put in a feature
request for the next version of emacs?  I know that fringes can be >1
column wide, so it would be nice if the header-line and mode-line can
do the same.

Peter