Hey look, Brawl+ when hitstun first came out!
http://www.youtube.com/watch?v=cjdgVmy1EU0&feature=related#t=2m15s
All lulz aside...
That's actually a pretty interesting idea. Being able to control or plan for some of these things would actually add a new dimension to many character's games. It might have some adverse balancing effects though (as in Luigi having godly recover if the misfire could be mastered). We'd have to be mindful. But I'm all for tinkering with it if it's at all possible.
The only random aspects of the game are (correct me if I'm missing anything):
1) D3/Peach projectile
I like the above suggestion, though the number might have to be higher.
2) G&W hammer
Make it go in order? He'd have to use it 8 times to get to the 9, so as long as you keep the pressure on it'd be hard for him to abuse it. Spamming through the numbers after knockback/kills might make it too reliable though.
edit: forgot this!
3) Luigi misfire
Above suggestion once again.
4) moves that trip
Having moves trip only at the tip would be cool. Remember that the game keeps track of moves that barley skim the opponent (when the sparks come out)? Perhaps if we could find that in memory, we could have it trigger a trip on said moves.
Another idea would be to have tripping attacks only trip when the opponent was running. That might make short range trip moves too useless though.
Just throwing some ideas around.