Who wants to play a game? Here's what I have in mind:
A personal union between two crowns is proposed by a member. Other members then suggest various ways that personal union could come into being. The person who proposed the original challenge then picks which idea they like the best (my personal recommendation is whatever sounds the most historically plausible, and whomever suggested it gets to present the next union challenge. And everything repeats.
Here are the rules:
- Historical titles of the same period only. No 'Argead Macedonian-Brazilian Union'
- Titles need not be of the same feudal rank. Duchies, kingdoms, counties, empires, marches, baronies, whatever. But no going up the same kingdom (so, no Duke of Aquitaine-King of France').
- No need to propose that the Union lasts more than a generation. But it must last at least the lifetime of its intial ruler.
- Inter-religious unions only are acceptable within a religious family (protestant-catholic is okay, coptic-hindu is not).
- The proposer may suggest some restrictions, such as a time frame, but try to be generous about it.
That should be enough rules. Basically, play with CK2 rules and you should be fine.
The first challenge: Have the same person be both King of France and Holy Roman Emperor. Only restriction is that it must be after... 1066 (to stick with the CK2 inspiration).