OK, FWIW, here's another idea. This doesn't respond to a general need for
multi-line headers or multiple headers or any of the other things discussed so
far. This is just an alternative breadcrumbs approach for Info.

The idea is to use the mode line, not a header line, for breadcrumbs. Please try
the attached patch, which is against info.el from today (it also works fine
against the 95 pretest). It will take you only a moment to try.

By default (in this patch at least) breadcrumbs are turned off. You can turn
them on using `Info-breadcrumbs-mode', which is in the Info menu as `Toggle
Breadcrumbs'. (That menu is of course also on the `Info' minor-mode lighter in
the mode line.)

When breadcrumbs are shown, they are all that is shown in the mode line. Mouse-2
on a node of the breadcrumbs path takes you to that node. Mouse-1 anywhere on
the breadcrumbs brings up a `Breadcrumbs' menu, with these items:

 Set Breadcrumbs Depth
 Toggle Breadcrumbs
 Previous Node
 Next Node

The previous and next items are there only when there is really a previous or
next node. Setting the depth here (first menu item) does not change the value of
option `Info-breadcrumbs-depth'.

It's pretty simple - give it a try; you might like it. The mode line, like the
header line, is always handy - no need to scroll.

A possible change: Add a menu item `Customize Breadcrumbs Depth' for customizing
`Info-breadcrumbs-depth', the default depth.

Another possible change: Put back the size indication mode when breadcrumbs are
shown. I don't miss it (the scroll bar is enough), but you might want it. There
is probably room for it, even for manuals that have several levels and long node
names.

Another possible change: put back the read-only/writable indicator. Or perhaps
just turn off breadcrumbs mode whenever someone edits an Info node.

I don't think you'll miss any of the other stuff that is normally in the mode
line. I don't.