Thanks for the input! I searched the form before my post, and found some great ideas, especially about Brevoy, but not so much about Choral and his vanished house that I liked.
My current, unfinished ideas (which already changed again since my first post) are the following: I do not really want Choral to be just some red dragon, because it seems too obvious since it is even a common rumor in Brevoy and makes the question about who exactly are the Rogvarias complicated - they don’t really feel like dragon offspring to me. I am thinking about making him a mere human who is not satisfied with having a huge army, a kingdom and being a mighty but mortal warlord and wishes to be a great red wyrm, similar to other mortals wanting to be a lich or a god. This fits his Ioberia-background with all the dragons, plagues (his quest would start before the eruption of the drakeplague, so the idea to avoid plagues by becoming more than human then seems plausible) and empire-in-demise theme. From there, I will most probably go along with the “evil-pact” thing. So conquering Brevoy would then be some kind of test, “sleeping” for 200 years and sacrifice his own family a price, perhaps I add other things here. Like sacrificing his army and especially the dragons, maybe even make him “possess” the bodies and the powers of the latter somehow.
I’m yet a bit unsure about the pact-part however. It’s a bit overused and the obvious path, but without it Chorals action and the vanishing just seems too strange. I don’t like a fiendish theme here because it would add another one to Kingmaker, which is already kind of overloaded with such in my eyes. For now, I think I prefer a First-World theme around the Elder Ones. Then it would overall first be a story mainly about exploring and mortal empires until the end of part 5. In which I think I’ll start a Brevoy civil war after part 3 and go a bit Game of Thrones from there. Otherwise, all the info about Brevoy would be a bit of a waste and regarding powerlevel it takes away the “superpower” Brevoy and adds a bunch of nations more in line with Mivon and Pitax and on eye level with the PC-kingdom. Afterwards a constant struggling with First-World-problems (pun intended) would follow (as opposed to fey and devils if it’s about an infernal pact, which kind of stretches it for me), as a opportunity for the PCs to be really heroic and rise up to be the rulers of a realm containing their own, Pitax and Brevoy. I’m unsure if and how I should connect Choral and Narissa if I follow this yet. I although don’t know if switching the Choral theme from fey to cyclops would be more fitting. On the plus side, it would make it easier to deal with Skywatch, another riddle I would like to present an answer for. That would be a particular good option if there is a TPK at Vordekai’s (we agreed to punish the Kingdom if there is a TPK, but besides that continue with a fitting second group in this case), in which case I would deny the PCs the Nomenhights and implant a little new undead kingdom there, which has a focus on conquering Ioberia instead of the west though.
However, this are all vague ideas. I don’t even know if Choral should not rather be a dragon from the start nonetheless and the mentiones idea to kind of replace the jabberwokky with him or some offspring is tempting. It would went nice with the vorpal sword theme and I just hate the look and some aspects of the jabberwokky. The idea about Brevoy being some kind of refuge to avoid the Drakeplague is also nice, but this needs some adjustments in my eyes to look good compared to dragons like Sjohvor who just survived it anyhow. Moreover, I especially have trouble with the Rogvorias if Choral is a dragon, because I see them unfitting as dragon offspring. Generally the Rogvorias are one of my main problems, some of my PCs are also interested in them (I can’t blame them) and I want to come up with a particular good explanation here. I brainstormed some ideas like a mass “trap the soul”-spell with connections to Vordakais Soul Jars. I even considered some kind of “Familicide” spell like Vaarsuvius used in OOTS. However, everything besides the doing of some demigod-like power doesn’t worked out well in my eyes yet.
All of this has quite some flaws left. And I'm not done yet with wwaging concepts. My latest thoughts spiraled about if it’s a good idea to flesh out the two dragon allies of Choral, because until now they are plain monsters. One idea is: they stayed in Brevoy instead of Choral (whatever he is). The Rogvarias are mere humans dummies, but one dragon always kills the current heir, takes his place for a mortal lifetime, then repeat it. It was killed by the pact-thingy that killed the Rogvarias. The other is more magic-prophecy focused and foresaw the attack. It lives under Starfall and pushed some kind of panic button for magical defense. And I still need some good ideas for Chorals minions once he returns. Just some humans is boring and Kobolds are a bit on the weak side.
So my thoughts about it are overall quite obvious in a state of chaotic beginning yet.