I think 20 20 will ruin itself TBH. Something SP Fleming said this week was that it if you were playing it day in, day out, it would get very montonous, which I agree with.
ie. slog, slog, slog, slog, wicket, nice shot, bang, slog etc
The actual beauty of the game (such as the swings and roundabouts, little battles within the battles you saw in the Ashes last year, or pretty much any competitive test series) will remain in test cricket and to a lesser extent ODI. 20 20 is just a hit and giggle with, at the moment, quite a novelty value.
If people were getting bored with ODI format (that they tinkered with and made it worse IMO), can you imagine how fast 20 20 will become a three hour waste of time?
Saying that, I can see the value of it at the moment. You always thought about batsmens' mentalities near the end of the innings in ODI's when they weren't having a go and getting as many runs as possible. You can see that happening now. More.