Well it could be the announcement of plans to abdicate in the near future, or perhaps plans that when she does die or abdicate, that Charles will immediately abdicate to allow William to take the throne.
Or if we're reading into the 'constitutional implications' then perhaps they are changing things so William can automatically become King once the Queen is gone rather than Charles, either through nomination by the existing Monarch or otherwise.
There is a lot of demand for William to become King and it would do wonders for the perception of the Royal Family.