Charlotte's future husband, if she has one, is likely not getting a dukedom at all - since they are the highest-ranking hereditary titles, they have only been handed out to princes in over 100 years. One was offered to Winston Churchill after WWII, but that was an exception. The only way that it may happen with Charlotte's husband is if she becomes the heir to the throne. Otherwise, if he gets a title, it'd likely be an earldom.
Prince Edward has taken over a lot of his father's duties, including much of those dealing with the Duke of Edinburgh's Award, so I think the family, Charles included, is on the same page as to what will eventually be given to Edward. Edward (and Sophie) will likely be the strongest support for Charles, other than the Cambridges, when he becomes king. And the dukedom will cease to be royal once it gets past Edward's son.
I know! My history-loving ass sure likes reading up on the whole thing, though. At least now, the titles are limited to being just titles (and land/property for most and the possibility of being in the House of Lords) and not, like, having the power to raise private armies from your lands in order to fight some other noble with his own armies or a disliked monarch.
ETA a small, related tangent: When Elizabeth I came to the throne, there was exactly one duke in all of England: the Duke of Norfolk. She had him executed for treason and, for the next 30+ years until after her death, there were no dukes in England. The potential power of a duke was too much of a hassle for her, so she just avoided it. There were barely any marquesses or viscounts. She was just done with peers of the realm having any sort of power.