I love, love, LOVE the MASSIVE amount of irony and hypocrisy coming from some people in this thread, first of all.
Next, I might be wrong, but I don't seem to remember many (if any) tournaments being particularly nitpicky with their stalling rules. I'm sure a bunch of guidelines were used at specific tournaments (or even in specific regions), but the vast majority of tournaments, IIRC, just say something like 'no excessive stalling' or something like that.
Smash has relied on completely subjective judging on this issue since day one. We don't NEED a clearly defined way to identify the threshhold on which something becomes stalling. Why? First, no one's going to jeopardize their tourney chances by skirting that close to the line. Someone enters a tournament that says no infinites, no one's going to even go near the territory of grabbing with DDD on those 5 characters at all; they won't even bring up the second grab. They risk the chance of having a TO called over, and even if they don't get kicked from the game, they're on high watch from then-on. Someone goes to a tournament that just says 'no stalling' with JP in Melee, they're not going to do the rising pound stall. It's way too risky vs. the reward. Point blank, the subjective judging that we've used for would completely work for this issue, and an insta-ban wouldn't let the potential of the technique see how tournament play is affected.
Basically, it doesn't matter that we'd need a time limit now. Someone wall-bombed in Melee, a TO gets called over but doesn't have any reliable sources on how many times the wall was bombed. His only solution is to view the match and make sure it doesn't happen more than 2 to 5 (whatever the rule is) times again, and 100% of the time, no one stalls because of the risk involved. With this, the TO could come over and say you can only use it for less than 2 seconds or so after he starts moderating. It's subjective, but a) I think most TOs can reliably count up to 5 seconds (lol) and b) the fact is, no one is going to even attempt to get that close when a TO is moderating.
It can be moderated using the same subjectivity we've ALWAYS used in Smash.
Edit: My harmless opinion that will get me yelled at: It looks like some people are throwing up some bad excuses for trying to ban something they deem 'too good.'