There are three possibilities here.
One is a general graphics browser -- that is, instead of being limited to
hypertext, go for hypergraphics. This would mean picking a graphics
standard and adding an anchor representation to add to it. As you say, a
line mode browser could just list the links from a graphics node.
Another is building a graphical map of part of the web. This is a good way
to navigate, but it is quite a challenge to decide which nodes and links
to put in and leave out, and where to put the nodes. Bear in mind that some
nodes have just a few links, some have hundreds. Trying to get the most into a
window and at the same time make it look natural is an interesting problem.
If it was computationally intensive it could be done off-line.
The third is combining the two above by making a "map" window for an existing
browser. This could serve the "History" function of showing where a user
has been, but with links off to other nodes too. As most people seem to prefer
to think of the data they browse as a tree, one could start by representing the
paths the user took as a tree, and then put in cross-links and links to
other referenced nodes.
Yes, its a great idea -- anyone want to implement it? :-)
Tim