I can think of one approach which would work efficiently.
Lets assume that each section is defined something like:
<SECTION>
<H> this section's header </H>
<SECTION>
<H> a subsection header </H>
</SECTION>
</SECTION>
First consider the case where a node is browsed independently of
other nodes. The style preferences define how to render the top
level header, and so on for each nested section.
Now if the node is considered as being part of a "book", the starting
level for the node can be defined by the context. As you traverse the
nodes that form the book, the browser keeps track of the level.
In many ways this is like the notion of context dependent navigation
links for table of contents, glossary etc. You could use an element
at the start of a node to define the starting level, or rely on
browsers propagating this property on the fly. The latter could even
be allowed to override the former, which is then treated as a default.
Personally, I prefer the explicit style in HTML and HTML+.
Dave