No doubt in my mind that a lot of people will be better off with lower carbs and 12 weeks at 800 cals a day will help them some to lose weight and from my personal experience will lead to much better BG control, my graphs from my Freestyle Libre are exemplary. To suggest it's a complete cure would be misleading. I've only ever increased my calorie intake from 800 to about 1200 with most of that 400 extra being protein, but in my case it's enough to start mg BG spiking a bit.
I wish that people's expectations are handled better because there could be some disappointment which could lead to this approach being ignored in the future.
Something none of this hype seems to cover is the state of the pancreas in the first place, the pancreas might produce normal amounts of insulin, as does mine (3 c-peptide tests in last 2 years), but what about the pancreatic beta cells which are responsible for producing insulin. Also, as there are tests for insulin resistance, I'd love to see before and after.