Some friends and I are working on extending the GDMBR south of the border. Still a lot to go, just some small sections have been confirmed so far.
My guess is that the first 200 miles are going to be ready by this time next year.
At the same time, we are working on a Garmin GPS map to use as base:
https://libreriacrisol.blogspot.com/p/mapa-de-aventura-en-chihuahua-para-gps.html (the map covers no only the route but all Chihuahua state and surrounding places, if you are interested in the map but don't read Spanish, just look for the dropbox link)
I'll try to post notices for the next expeditions in case someone is interested.