Yeah, there is no reason to replace AF1 for a long time. When it happens, expect something big, with four engines, fast, and American-made. I seriously doubt that they would buy something european, simply b/c it would be simpler to keep it in the US, security-wise and all. Still, there is no reason to replace the current ones(VC25's??) for a long while.
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation