There doesn't appear to be an answer because there doesn't appear to be a question !
Perhaps slightly unwittingly, you put your finger right on it. Quote: "practical agreed systems to replace the ones we already have ..."
If as you write we already have them and they are ' practical agreed systems' then nothing, apart from the name or title of the replacement issuing or supervising authority, needs to change. In this respect, the CAA clearly has the means and the expertise to manage the takeover..