Although I do support your view of motive and murder, I honestly think you'd have to be very, very silly to murder one of the most famous women in the world (at that time, at least) in such a cack-handed manner. Leaving behind so many 'clues' that it would become the subject of hugely expensive, public enquiries and endless speculation about murder and the Royal family - which, whoever and whatever they are, wouldn't serve their purpose at all. If such an operation is the work of secret services in this country then God help us all
They really should be fired. To a great height.
In respect of Diana's potential marriage to Dodi - who knows? I have no idea if that was on the cards or, given Diana's charming, but nevertheless erratic nature - just a happy fling. She'd only known him five minutes and I believe their relationship was a little engineered by Mr Al Fayed senior rather than a fairytale meeting.
Still, if it was real and a massive threat to the monarchy I would imagine either exile or the threat of being permanently parted from her sons would have been sufficent threat to deter any such marriage. Despite her obvious problems with Charles, in TV interviews she appeared to very much want her son to be King and therefore part of this establishment. I don't think she'd risk that ambition - it appeared something she wanted a great deal and said so publicly.
Such options - exile, reduced or no contact with her sons - wouldn't be the first time the Royal family have packed away their more embarrassing family members (i.e. Edward and Prince John).
Mohammed Al Fayed also has enormous motive to create waves. Firstly, he lost a beloved son - something few people give much thought to - as the spotlight was on Diana. I don't think much thought was given to Mr Al Fayed in this very sad event. Additionally, he has constantly tried to get British citizenship and has been rebuffed. It's a fairly well-known fact that this has become a very sore point for him.
As for Harry's link to whatsisname.....James Hewitt, isn't it? I admit to having some intrigue in this until recently. I happened to see both William and Harry on a news program together and Harry pulled some kind of facial expression and became the image of Charles. It quite startled me! It really was so strong that I had no choice but to abandon the Hewitt theory.
Red hair is a Spencer trait anyway, and I suspect as he grows older, the 'Charles' in him will be more apparent.