"Fake" XDF disk support works now
What this means is that XDF disk images formatted as 80-track 23-sector-per-track images will work with XDF code that honors that format; however, I've not yet been able to test with "real" XDF disk images (ie, disk images created with DiskDump using the experimental --xdf flag).  "Real" XDF disk images almost certainly need more work (eg, setting all the sector IDs properly), but the groundwork has been laid.