Playing every thing in a day can make it end very late and also your system doesn't allow the 4th team to participate in the playoffs.
You could allocate less time for playoffs (as ombrack said) and force teams to play within this period of time to make it less boring.
I think we can fuse the s21 idea and the current system as:
Game A 1 vs 2 (with map pick/ban advantage to 1)
Game B 3 vs 4 (with map pick/ban advantage to 3)
Game A winner goes to final (and has pick/ban advantage in the finals)
Game B looser is out
Game B winner plays Game A looser in Game C
Game C winner goes to final
This format can be made not boring. You can force all games to be played in 1 week. A and B on day 1, C on day 2 and final on day 3, days do not need to follow each other. We can even now merge onto your original idea and play game C and final on the same day.
This makes the season relevant because ending at the top of the tables gives you advantages in the picks and/or a direct chance to reach finals.
edit: heh, pretty much Setsul's idea but 10 minutes too late...