Hi mikethepike, just returned on Saturday from 7 days hiking from Mt Hopeless south to Arkaroola. It marks the completion of a Flinders Ranges traverse: the Heysen Trail then three weeks walking from Parachilna Gorge to Mt Hopeless. That very northern section was the hardest of the three north of the HT walks, but there was water almost everywhere, finding drinking water was no problem, even enjoyed a few swims. Described by locals as the best season in 40 years. Flew by helicopter from Arkaroola to Mt Hopeless, then walked across the gibber plain, Mt Babbage, into Hamilton Creek at Terrapinna Springs (gorgeous swim), following the creek south west for three days to Greenhill Well, south to Daly Creek and Yudnamutana Gorge, the Armchair, Mt Painter and back to Arkaroola. Had intended to fly from Arkaroola to Moolawatana by airplane, but the airstrip was closed from rain damage. This would have been a very different walk without the flowing Hamilton and Yudnamutana Creeks, in drier times water drops would be necessary. Unlike your plans, didn't walk across the Mawson Plateau, another time.
Last year in the Arkaroola to Angepena Station section we walked through Mainwater Pound, climbing Benbonyathe Hill, Gammon Hill and Arcoona Bluff. It was also a wet season, so again drinking water was not a problem. Due to widespread road closures (all roads north of Hawker) flew by aircraft into Arkaroola and walked out to Angepena, the roads south to Hawker reopening the day we reached Angepena. It was described by locals as the best it had looked in 20 years.
The year before we walked from Parachilna Gorge to Angepena Station, climbing Patawarta Hill, Mt Tilley and Mt Hack. It was dry, drinking water from old tanks, dams and waterholes.
(for the benefit of others reading this and not particpating in mikethepike's walk, premissions from landholders are required for each section, but the landholders also have knowledge of the current status of water/tanks/dams. These are very isolated walks, you will likely not encounter other people.)
There are some blog entries here:
http://jez-hiking.blogspot.com/search/label/Beyond%20the%20HeysenHope you find some good walkers. I'm 34, a regular walker and pretty fit, but that last week was tough, daily distances not that great, but walking times long. Lots of bush bashing and hot, steep climbs. If you are prepared for that and water, you and your companions will be all good. As you say, the best the Northern Flinders and Gammons has looked in a very long time, you'll love it!