I'm actually working on a North Sea/Baltic ATL. It starts in 1042 but include the Hansa later "buying" the Royal power, resulting in what you could call a "commercial monarchy" ruling both the North Sea and the Baltic. But I still need quite a lot of research and details and is far from posting.
But concerning the Hansa, the basic idea is, that the Hansa bet on the right "horse" in a royal dynastic stride and understand to stay in the saddle. The result being the landowning aristocracy to a large degree loosing its place as society cornerstones to a trading oligarchy - but still in a royal context as before absolute monarchy was implemented in many European countries. In many ways it would not be unlike English parliamentarism, but with merchants having a more prominent and direct role, but expanded into a North Sea - Baltic Empire. How much you would call that the Hansa is a matter of taste - de gustibus non est disputantum - but at least it is big!
Regards
Steffen Redbeard