I do not see the benefits of a low calorie intake AFTER the Newcastle diet has done it's work. It is possible to be eating 800 calories a day containing only carbs and that wouldn't be good?
Keep the carbs under 100 grms and the same with protein and then the amount of calories is meaningless unless overeating is happening. I lost three stone WITHOUT counting calories because I counted carbs and protein. The fat content didn't matter because I ate till i was full and no more.
I think it's worth addressing the two points you mentioned.
Even after the Newcastle diet, even if reversal is achieved, some of us want to continue to reduce our BMI to a 'normal' number.
I certainly wanted to, and also found that I felt a lot better, could do a lot more exercise, and my lifestyle greatly improved. So I didn't overeat during that period either.
I also think you are getting a bit fixated on imagining that everyone then seems to continue to low calorie after.
Obviously, having achieved our targets, we eat normally, low carb is for life, low calorie is to achieve a specific target usually.
When that target is achieved, it's time to move onto a maintenance diet.
I do agree I don't 'eat until I'm full' though.
That was a habit that I desperately strove to break, and I saw eating until I was full as the thing that got me where I was, so I now eat enough, and if I'm not 'full', I know it's simply a state of mind,
If I gain weight, I realise I'm overeating, if I lose weight, I realise I need to eat more.
(As to eating 800 calories of carbs, I doubt any meal plan would consist of that, all diet plans are balanced)