But as leoreth said, Paris deserves its BFC. If you put another city in that area, you will destroy Paris, Amsterdam, and Frankfort. I don't believe it is worth it to place Aachen, even though it was so important to Charlemagne, and the early HRE...
Well, an idea would be, to have Aachen, and then later have Berlin pop up and make Berlin the capital. You would then make Aachen turn into a village, and Berlin would get all of Aachen's buildings and culture. (transfer of power).
idk; food for thought, and yes its possible to do this, believe it or not
But Krakow definitely needs to be in. To all Poles, what is the oldest city in Poland?