Except, what you said, and I quote, was "In my opinion, the Duke and Duchess of Cambridge will name their child with the name of a Hanoverian/Windsor King or Queen."
The Hanoverian monarchs were George I - IV, William IV, and Victoria. The Windsor monarchs were George V and VI, Edward VIII, and Elizabeth II. There is also the Saxe-Coburg and Gotha monarch, Edward VII, who was in between the two houses. That leaves us with the names George, William, Edward, and Elizabeth.
Even if we say that William, Elizabeth, and Edward are simply Hanoverian/Windsor names, ignoring that they have also been used by monarchs in other houses, Charles, Anne, Andrew, Henry, and James (all the other names of monarchs used in the Mountbatten-Windsor family) are not Hanover/Windsor names. Charles, Anne, and James are all Stuart names, and Henry is most recently a Tudor name.
If we're going with the idea that they're not going to use a name already in use, that limits them to just George and Victoria for the Hanoverian/Windsor monarch names. They have more options if they broaden the scope a bit - as has been done in the rest of the family. In my opinion, it kind of says something in that the two names that have only been used by Hanover/Windsor monarchs haven't actually been used by the Mountbatten-Windsors. I wouldn't be surprised if we've left George, Victoria, and even Albert behind for a bit as first names simply because the family became so saturated in those names and variations of them for so long.