Technically M&B already has less of the feudal levy army and seems to have a little bit of a standing army going on.
I mean there isn't a single state army loyal to the head of state alone but a medieval army wasn't constantly on the field in times of peace like what you see in the game.
Think of the difference between Crusader Kings and Europa Universalis.
In CK levies are only really raised in wartime and have to be quickly gathered together to form a cohesive army, whereas in EU the standing regiments are already raised and placed wherever you want.
So if by a more professional army you mean a more loyal state army then that would be something you'd want for a more centralized state, at the cost of increased maintenance.
Don't get me wrong I love the idea of having of having a professional standing army taking on the feudal system but you gotta make sure it doesn't throw the game out of balance.