Well France are still big so it will likely continue being a great power if it it unifies, of course France will be more limited in any Italian adventure, but the biggest weakness are if Bugundy still comes around it size are comparative with this lesser France, beside that France will be less able to influence the popes. But I must admit I have a hard time seeing France centralise without having/gaining control of Occitania, so likely the POD which create this are more succesful Normans, which weakens the French throne enough that France end up as the HRE. We may very well see the Emperor expand his overlordship to France. So we may see a France which goes the way of Arles and medieval Italy. Of course expanding the HRE will make it even harder to centralise, through Frances position are much to integrate into a common state with Germany than Italy are.