Sod the Nordic League if you want, on reflection I drew up the Southern League and there's mouthwatering football here. Qualification based on who is in Europe - in the Champions League quali stages or the Europa League playoffs round.
The only question is how many teams you want. This is a 20 team league, it's the Champions League (including qualifying teams) and later Europa League qualifying rounds (playoffs and 3rd qualifying round), less four kicked out by yours truly on a principle of kicking out teams that aren't as big names from the bottom of each country's qualifying but leaving every country with one. Buraspor from Turkey, POAK from Greece, Levski Sofia from Bulgaria and Rapid Bucharest - the only team from the Europa League Playoff round to not get a slot. I admit that Rapid Bucharest do seem an odd team to choose, but I wanted to make sure each team had one or two.
Skendija (Macedonia)
Mogren (Montenegro)
Partizan Belgrade (Serbia)
Red Star Belgrade (Serbia)
Maribor (Slovenia)
Fenerbahce (Turkey)
Trabzonspor (Turkey)
Besiktas (Turkey)
Otelul Galati (Romania)
Vaslui (Romania)
Steaua Bucharest (Romania)
Skenderbeu Korce (Albania)
Borac Banja Luka (Bosnia and Herzegovina)
Litex Lovech (Bulgaria)
CSKA Sofia (Bulgaria)
Dinamo Zagreb (Croatia)
Hajduk Split (Croatia)
Olympiacos (Greece)
Panathinaikos (Greece)
AEK Athens (Greece)
This would never happen in real life due to UEFA's one league one country rule (I would like to see some joint leagues, just to see less, better quality football) and the possibility of World War Three happening in the stadia, but this could be a quality league. It might even wind up on Serie A or Bundesliga level.
EDIT : If there's a Scottish-Irish league, bearing in mind we're not having one league one country, I'm going to fly up adding Cardiff City and Swansea City to make a sort of Magners League of football. It could become a league of Eredivisie strength.
So that could mean
Loadamoney MLS or J-League
My 20 team Baltic/Southern League
Eighteen team SPL + stronger Irish teams + Cardiff and Swansea City (name : Guinness League?)