There’s a reason that characters hit with a focus crumple enter into an aerial state before they fall fully to the ground in Street Fighter IV. Not only does this make the timing on the next hit targeted at them slightly tighter than it would otherwise be, but it also prevents an endless chain of focus attacks from crumpling opponents ad nauseam.
Nintendo took this into account when they gave Ryu a version of this powerful attack to bring up against the cast of Smash, but there is a way around it in some situations.
Consecutive crumple attempts pop up opponents only if the focus attack isn’t held for its full duration, or if Ryu faces his opponent when the move’s animation finishes. This second condition can be finnicky and will occasionally allow for a handful of back-to-back crumples at specific damage ranges, but it’s inconsistent at best. If allowed to release on its own after reaching full capacity, and with Ryu’s back to his opponent (this part is key), Ryu can indefinitely crumple some characters; Charizard and Donkey Kong have been confirmed as potential victims.
Actually pulling this off in a match won’t be simple since Ryu has to be practically inside the hurtbox of his opponent when his first focus attack finishes, but once he gets going, the combo is essentially free. Check out the video below from Dezmu to get a feel for the sort of timing that this requires.
Source: Dezmu and a shoutout to KGA’s Lenny for sharing this.