Lucca
I wonder if, given he was such a prominent figure, he had in mind to publish his diaries as a book has he lived ? Pure speculation obviously
But everybody kept diaries in the days when Mountbatten was keeping his. Diaries of significant, and insignificant, people have been published (suitably edited sometimes) for decades. And hugely valued by historians as a primary source.
You rightly say, it's speculation, Lucca, but I wouldn't think that he would have spent much time thinking that something he did as a matter of course might be published. If he did think about future publication, I would also think that he would have tried to keep any potentially damaging revelations out of it. He was deeply involved with the RF, after all. Why would he want to tarnish them?