Nobody can do this accurately without the kind of data that examiners get access too.
They can't even have a guess until all the papers have been seen. They certainly can't have a guess without knowing exam boards!
It might be that boundaries go up a bit, because teachers have a bit more experience teaching new spec and there's a bit more information out there for students to go on. It might be that the exams are slightly harder, so grade boundaries stay the same or even go down. Or there might be a huge jump! There's nowhere near enough data available to see a trend and make predictions.