I couldn't retrieve the references you gave for managing history
using HyTime. In reading through the HyTime architectural forms
and background material, I didn't see anything directly relevant
to issues such as what can and can't be scrolled away.
My suggestion for extending the LINK attribute is a very natural
extension to HTML and builds on earlier precedents. We have
recently developed a flexible scheme for expressing hypertext
paths, where paths are themselves HTML documents. The ability
to specify images for such navigation buttons is already popular
in the WWW community, and my suggestion extends this to include
a document toolbar, using the LINK element.
HyTime's location ladders and event mapping etc. are largely
orthogonal to these ideas. Indeed, it is already clear how to
add the HyTime clink architectural form into HTML, as an alternative
to the current HREF and SRC attributes. Perhaps you could make
a more concrete proposal for how this would effect issues such
as management of history and visibility of navigation buttons.