Got back yesterday from the above hike.
Descent via the South Bass trail to the Tonto trail then east to Indian Garden. Up to the South Rim to resupply and back down. Then east on the Tonto to the New Hance trail back up to the Rim. Total distance about 105 miles.
Trail conditions on all the trails are poor to minimal in places as the trails are not maintained and have not been in some parts for a couple of decades (no money). There is heavy overgrowth forcing reroutes and trail finding as well as lots of washouts and erosion issues. This is eased somewhat in between the intersections between the Hermit Trail and the South Kaibab in the middle of the hike and then back to the same on the east end of the hike. There are a few places where if you slipped and slid off the slanted trail death would be certain and lots of cool exposure looking down into deep ravines and off cliffs.
The ascent up the New Hance was a good challenge at 4400 ft with washed out and rock slid trail as well as overgrowth. Lots of big boulder step ups, slippery ground with the standard AZ marbles and seas of small rocks, loose rocks abound. Much harder than any AT climb for reference. In the rain going up would be dangerous and down would be far worse. Up in the snow might be possible but only for an experienced mountaineer, down would require belays/rappels in some places.
BUT... a great hike! The canyon to the west is even more scenic than around the main north/south rim tourist locations. And we saw only 2 people until the 3rd day. The best views in the canyon are about 30 miles west from the Bright Angel Trail. Way to the east there were also virtually no hikers. Unusually for the canyon there was WATER everywhere almost - so no big water carries. And we got rained on on 4 days - may as well have been on the AT ha ha. It snowed on the rim two nights while we were there.
Definitely worth it if you have the time and some desert hiking experience. We took 9 days but it could be done in 7 for sure if you are fit and willing to walk most of the day and not sit around gawking. Making more than 2 mph overall on these trails would be hard and in some areas it will be down to 1 mph or so.