That's a good idea (looking for kill set-ups). However, the example you gave should never work on any character since you can just SDI the uair. However, it could frame trap if the airdodge/whiff an aerial.
By the virtue of SDIng Dair/Uair, DDD should never use either move while off-stage vs. characters like Falco or Ganon. The reason that I mentioned it, however, wasn't to force the kill, but as a safe way to frame trap into it. If Jigglypuff air dodges through the Uair into DDD, DDD has Utilt. It doesn't work on account of Jigglypuff being able to DI away from DDD, but I was using it as an example. Set-ups aren't restricted to "guaranteed" and "not guaranteed."
When looking at set-ups, look at risk -- "What will happen if this doesn't work," reward -- "What will happen if this works," etc.
For example, using Dash>Dsmash to try and punish Falco's tech roll away from a Dthrow is a bad idea when both characters are at kill % because the set-ups results in Falco being able to kill DDD if the set-up doesn't work because the timing is slightly off -- especially if Falco accidentally power shields. This is as opposed to something like Dthrowing Falco by the ledge and charging Fsmash where a power shield is less likely and the other common form of failure is Falco being forced to grab the ledge from the shield push.
At the same time, player errors/habits also allow different punishes/gimmicks, which is why the former set-up can work on some players. With this in mind, neither set-up is a bad idea, and can ultimately be useful to the general DDD metagame. I'm not saying that guaranteed set-ups are bad; they're great and should be the meat of everyone's gameplay, but I've won more sets with a gimmicky Fsmash set-up than I have from Dthrow infinites. In other words, what I'm saying is that putting some gimmicky buns and cheese on the meat of sound basics makes a piece of meat into a cheeseburger.