The map files for XCSoar are XCM archives containing:
1. ESRI shape files (roads, rivers, cities, etc.)
2. A topology file to describes which shape files are available and how to render them (line thickness, point size, colour, etc.)
3. A waypoint file in CUPS format
4. A DEM raster map in JPEG 2000 format with accompanying world file.
All data is in the WGS84 datum.
One could easily use standard GIS processing software to generate your own ESRI shape files and add custom layers like sectional charts.
It just takes some time and tinkering.
Some info of what goes into the XCM map files and :
http://forum.xcsoar.org/viewtopic.php?f=19&t=918
Maybe I should set up another mirror for generating maps since XCSoar without maps is a deal breaker.