Now that would be a novel format. Giving the team top a rest day.Not for me. Top 2 going through would have changed the mindsets of every team and made it more enjoyable.
They still could have had 24 teams. 12 teams go through with the top 4 ranked teams earning a bye from the first round of quarter finals. So a massive incentive to win games and top your group.
Games for me would have been more open and attacking. An example would be the England- Scotland game. Both teams happy enough with a point as England are pretty much through and Scotland keep their hopes alive.
Giving the teams a bye would mean England would have been looking for the win and Scotland the same as 3rd would be no good.
Everyone wants to see exciting games and this format doesn't do that.
Keep it quiet. UEFA might just try it.