4 groups - 7 teams is actually okay. But swiss system looks much better in terms of fairness.
There are 27 Nations :/ Way too many teams for the Suisse system, would take too long and is open for a lot of bias
I'm sure that 2 or 4 nations will disband before the start anyway
First it would be better to have an even number for both groupstage system and swiss system.
With 28 teams, that means 14 matches by week, 5 rounds of swiss meaning that it will last 5 weeks to have 14 teams qualified. After that I suggest to do the classic elimination stage. The problem I see with 14 teams in the elimination stage is that there will be an odd number.
7 matches, so the best is to add 2 another nations in order to have 16 teams. I suggest taking both teams (among the 2-3 teams in the swiss stage) with the most rounds won.
Rules Summary :
Win 3 to qualify
Lose 3 to be eliminated
Always play a team with the same record
Never play the same team twice
And every sunday night you draw lots in order to know the matches for the following week.
If everything goes well, the whole tournament will last 9 weeks.
Week 1 to 5 everyone ( teams can be qualified from week 3)
Week 6 16 teams
Week 7 8 Teams
Week 8 4 Teams
Week 9 4 Teams (Final and Bronze, would be best to have the bronze match few days before the final)
Tbh, both system are viable, but after thinking the swiss format would be best. Because we all know that several nations will disband after losing 2 or 3 matches in the groupstage because they know that the qualification remains impossible. With the swiss system, even if you lose your two first matchs, you still can manage to qualify for the next stage because you will play against teams with the same record. That will prevent teams to disband.