Personally I don't think there would be an adv 3. I think they'd split up. It's one reason I'm okay with where SSSS ended. It's a nice calm moment and feels like a national end to the crew.
I imagine Sigrun not being swayed by Sweden and going home. Reynir might realize that his only chance of getting anything resembling training is to go to Norway with Sigrun and working with the mages there.
Emil and Lalli may take the Swedish proposition or might just go back to being cleaners. It is possible Reynir would stick with them - although I want him to go to Norway. Onni would likely end up wherever Lalli goes, or else take on a new apprentice mage.
Mikkel I could see going either way. I personally think it would depend on what the details are. I think he'd go with whoever he felt needed him most.
If there was an adv 3, honestly I'd be disappointed if it was Sweden. I really, really, really want to see what the Norwegian military is like and specifically to see competent icelandic battle mages.
For an adv 4 - I'd really like a swedish one that's heavily atheist. I would personally love for it to turn out that the mages aren't actually needed in Sweden and realize that it's not that the swedes ignore the gods' gifts - the swedes just honestly don't need them.
(Hrm okay so it might be interesting to see Reynir go through an atheist adventure before meeting a mage... Hmm.)
I don't know enough about Scandinavia to be comfortable even trying. Don't have the time/energy to research the geography and I'm kind of crap at it.
So if I were to write one, it would be based on the icelandic I studied and my years as a Heathen which were both more than a decade ago.
Which feels pretty terrible next to the fics by actual Scandinavians who double check details with their friends from other countries...
I would love to have a go at something like this, but I would want to do it properly, so it would require a lot of time. More than I have, probably.
I haven't even finished my ghosts-in-Iceland adventure.
I'm not sure if this is the direction you're going -
But this comment made me think of how coldly Iceland killed all those refugees.
Some will likely have become trolls, and it's likely that the ocean surrounding Iceland is full of a lot of angry ghosts.
and if you've finished I hope you've shared it I'm having trouble navigating this forum on my phone right now.