Very good point. I'm still not decided on whether I'd prefer the Danish team(s) to be able to get relegated and replaced with another Danish team or if a specific "Nordic League"-team should be made. I'm leaning towards the first right now...
Pros:
A) I think the swedes would like their Allsvenskan-teams to be able to win a spot in the SEL. And if Swedish teams can go out - so should Norwegian and Danish. Anything else is silly.
B) You'd be able to build on a already existing fan-culture, front office organisation and sponsor-connections. You'd just be taking next years champion.
C) I fear for the development of the reserves of a "Nordic League"-team. The NT will not benefit from having those right outside the team put on the bench for a whole season.
Cons:
A) The quality of the team might not be as good as a new "All-Star" team would. As relegation is at stake some players might take their chances in their current clubs.
B) I'd would after a couple of years make the Danish league boring since the strong team would get stronger while the smaller teams would get weaker.
C) The teams relegated would have dramatic changes in competition.
D) It's a silly system really. During the season the leading teams in Denmark, Norway and Allsvenskan wound't know if they are fighting for a spot in the SEL or "just" the honor.
Perhaps some sort of play-off system between the best Danish and Norwegian team and the two best Allsvenskan teams could be made... I'm just thinking out loud here