I finally implemented lines and polygons in our PleiadesGeocoder software not so much for display of ancient roads as for making georeferenced feeds that show where we will have new data coming online. Here's an example feed and map, and a snapshot of the KML in Google Earth below:
Also new is a form for setting the location of any Plone content. Location is still stored in GeoRSS (Simple) form in PleiadesGeocoder (mostly to delay content migration), but the form takes GeoJSON. The new code I'm working on for Plone will be storing locations as GeoJSON geometries.
After we get a few bugs out, this will be released as PleiadesGeocoder 0.7 for Plone 2.5, and I'll get back to work on the next generation for Plone 3.