They could do the group winners and two best runners up as said. Obviously the likes of France and England would be more switched on from the start, but if that was the format, France would be out, Austria would be through, and England could have come close to being out too.
Lots of jeopardy and one less knockout round to win it. High risk, high reward. It feels better than only eliminating a third of the field after 36 games.
On the other hand, it could lead to a lot of dead rubber games because many teams will be out of contention for a top spot after two games.