I see only one problem with these play-offs, and that's: A draw will decide who gets to play at home in the final play-off match.
That seems really unfair.
Why?
In the group semifinals 2 seeded teams will play at home against 2 unseeded teams. Let's say Italy, Portugal, Ukraine and Austria are in the same group, where Italy and Portugal are seeded. These two are seeded, and will be hosts in the semifinal, exactly because they were better in the group-stages and were among the best 6 runner-ups. Portugal won 17 pts in the groups, Italy 16, Ukraine 12, and Austria didn't even make it to top 2, but they qualified via the Nations league.
So, it makes sense why Italy will play, say, Ukraine in Rome in the semifinal, while Portugal plays Austria in Lisbon. They are rewarded for being better than Austria and Ukraine in the group qualifiers.
But why should a draw decide who hosts the final? Say Italy and Portugal make the final and the draw makes Italy hosts. How is that fair when Portugal did better than Italy in the group stages (they won 17 compared to Italy's 16 pts)? It would have been much more fair if the final was played on a neutral venue.