When the going is good, I find myself waiting at many times for the bricks to pop - even while maintaining 2 or more simultaneous chains.
This can be frustrating, because valuable seconds can be lost waiting since you can't push up if you have too much going on at once.
It would be a cool thing if you could tap to turn off the delay - sort of a 'super explode'. That way, esp (i am guessing) in the arena version of the game, you could get a speed burst if you were doing chains or multichains.
The way I see it the long delay after x5 was put in to allow you time to try to continue the chain - not to punish the player for doing a chain, which can amount to large points over time. This way you could, if you are able to pull it off, build up a chain much faster than normal and closer to 'swiping speed' that you can normally pop blocks at.
If you found this too powerful a feature, for users that could quickly climb to, say, x40 or 50 with this in just one minute, you could tone it down by limiting the # of times, or making it a power that has a charging bar.