I think there was something in 'Project Thaw', and Richard Eden wasn't imagining it. This is entirely my own opinion, simply from watching what was happening over the last couple of years, thinking about what he said, and thinking about the people involved.
I think the people involved in Project Thaw were certain courtiers who felt it would be 'good for the monarchy' if they were 'seen to be forgiving', and certain republican-leaning politicians who welcomed the Sussexes early on as disruptors, and would be happy for them to be back within the RF structure in that role.
I think it fell down on two counts:
-KCIII, for all his faults, is not stupid. He may love his family (we see how he is with the Wales children, and have been told of him reading stories to his wife's grandchildren), but he has a profound appreciation of his constitutional role. He will not do anything that will jeopardise that, or the monarchy as a whole. He has spent most of his life as apprentice to a constitutional expert.
-Harry. He is almost the antithesis of his father in these respects. If he had the sense to realise how best to behave, it might have worked. However, he continued to rant against both family and Family, and accuse his father of unconstitutional behaviour. He has most recently vilified one of His Majesty's independent judges, because he did not get the result he wanted.
This is just my opinion - and also why I don't think Harry will be a working royal again. He may be back within the family (small f) at some point in the future.