Dealers don’t know for sure until the actual day or, at most a day or so before. Anything that they say before that is usually pure speculation on their part. They sometimes get wind of proposed changes, as recently happened with Subaru, but often things that they are told about don’t actually end up happening!
APs, with a few exceptions, have been on an increasing trajectory for a long time. Nobody knows, but my guess is that they won’t rise significantly more in the future, as the APs currently being asked must surely be pricing a lot of potential Motability customers out of the scheme. If they go much higher more and more people will start to look elsewhere.