I think it's a bad idea because it would be an attempt to set the reasons as to why the Governor General exercised her power at that time. The Governor General is not trained in matters of state. She does take advice; however, it seems to me that any set of reasons would necessarily have to be drafted primarily by others and not by her personally.
I think the exercise of discretion is her personal discretion. She does take it upon advice, but I think it is exercised by her. I think the requirement that the Governor General then write or prepare her personal reasons may cause difficulties, and I do not think it is necessary. Because the range of considerations is complex, they are difficult and may evolve as subsequent circumstances unfold in later terms.
Again, I believe there's been some discussion about this requirement. On balance, I don't favour a requirement of reasons.