That video showcasing d throw -> u air is nothing new. We've always been able to do that. All that video will do now is maybe teach people to learn how to DI d throw
Here's the actual hoo hah.
Zelda's
real hoo hah is actually done by reading DI behind us (like anyone who actually knows how to play against her will do) and doing double jump > b air.
This'll kill near the ledge and is way more reliable than d throw u air, but harder to pull off (it's srsly like frame perfect.)
What's awesome about d throw > b air is that its kill percent generally maxes out at 68% and works on most high tiers. It also works out of d throw even before then, but just for damage. What's even better is that they're still DI'ing backwards when it hits them, which doesn't help their case at all. I've even done this to Zylach's Corrin offline.
In the end if you nail anyone with d throw > u air, chances are you're playing someone who's inexperienced or just a moron