The supersub just adds more complication. It's pretty useless and even if decided after the toss you would need a larger squad and one player missing out standing pointlessly in the dressing room where he could possibly be playing domestic cricket.
I disagree with the way the powerplays are being used. It could work like this:
The mandatory 10 over period stays as two fielders on the boundary. The remaining 2 powerplay periods of 5 overs should be used by both sides. This for example means the batting captain chooses when he wants it put in place, and the fielding captain also chooses one of the five over periods. The toss determines who has first choice. One captain wins the toss, he obviously chooses whether to bat or bowl. He then chooses who has first use of the 5 over powerplay rule. For instance he chooses to bat first, and says I'll take first powerplay decision, he then has to put it in place before the thirty over mark. If he doesn't the fielding side will get possession of both 5 over powerplays. If this was actually put in place which I highly doubt and results in all of them being used in the first 20 overs again, then the ICC should first remove the any powerplay rule and go shoot themselves.
I only wrote this because all captains use it in the 20 over period and is boring, so if both sides have an equal choice they might choose differently. A scenario where it works alright: If the side batting starts by losing a few early wickets, then they might wait until the 23rd over for example to give themselves some time to re-group, see the ball and take advantage with their eye in later. Etc, etc, etc. Sorry for the long post.
*Didn't see the post above mine basically suggests a similar idea, it took me a while to think of and write this one and it must have been posted during that time*
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