In the end I went for all monarchies in the moonshaes are a form of elected monarchy (except for the high king and now callidyrr which have hereditary monarchies).
So the clans elect a king from within a hereditary dynasty. This is just a formality however and in almost all instances the title passes from father to eldest child unless they are deemed wholly unsuitable (like Tristan due to his age and behaviour).
I figure the current and middle ages behaviour of Scottish nobility was all derived and inherited from exposure to England (via conquest or just imitation) so I ignored almost all of that and went back to a time without a hereditary monarchy where the clans owned the land. The king therefore had to keep the support of the clans or else risk being deposed and so a peripatetic monarchy helps a king do that (spending time with all clans).
The king is therefore more of a peacekeeper in early moonshae society. Centrally powerful kingdoms like callidyrr eroded the power of the clans completely and have all but removed them from society. Corwell is less centralised than callidyrr and so has turned the clans into a form of hereditary nobility (making them barons of a sort but the title is owned by the clan as a whole). While moray is a weakly centralised monarchy and so has remained in the same ancient clan structure of the moonshae isles (with a few exceptions).
I tried to make it as workable and fluid as possible within the bounds of history using what information was available on the moonshaes (callidyrr had Earl's so that were feudal nobility, corwell had clans voting for a king so they were at least part tanistry, moray had no castle so was not centralised at all).
I agree the opportunity for intrigue is greater in moray but I don't think the ffolk are like that. I'm not sure any of the clans want to be king really, it's hard work and they don't gain much more power than they have now. Intrigue is much more prevalent in callidyrr with the significant tethyrian heritage.
OK, here's a weird one ... not sure I should bring it up. Have you looked at Realmspace, pages 55-56? Curious about Omar McDauphin, now a stone giant? Curious about the origins of the Dark Moon assassins? Curious where Iron Keep Bay came from?
I have looked at Omar macdauphin and I decided that the mention of his events being recent was a mistake or a relative version of recent. After coming up with a timeline for everything I figure the northmen conquered Oman in 761 dr and that Omar macdauphin couldn't have a castle on the island after that date.
So I made the disappearance of his castle leave a huge hole in defences on the island and allowed the northmen to conquer it. The northmen invasion prompted his badly worded wish which inadvertently made the invasion successful.
The dark moon I have as a wolf shape shifting group of assassins that live in the feywild / plane of faeree, and have been used to kill a number of ffolk and northmen kings (they tried to kill high king tanner (or perhaps byron, I forget now). They use the moonwells and faerie crossroads to get where they need and then change into a wolf and eat their target. Those who fail to kill the target are killed so many flee into exile.
I'm very interested to know your plans for the dark moon. I am conscious that I likely violated canon but could not resolve that semi realms resource to the reality.
A century ago (which I think is the timeframe it gives in realm space) contradicts novel lore regarding Oman, it also goes against the trend of declining power in the ffolk kingdoms and a lack of cooperation among them. If a single ffolk kingdom were able to take back a portion of Oman from the soon to be most powerful northmen nation in the moonshaes then the present of the moonshaes would look very different.
So I decided a century could have meant centuries, or perhaps that source was written a long time ago and described an event more recent to that.
Just my thoughts, I'm more than happy to discuss all the sources and my reasoning and potential developments if you want (email is fine if you want to not give away any hints)