It looks like you're getting them to jump/run into the ending frames of Forward-B rather than outright punishing endlag. That makes this mostly exclusive to (l)edgeguarding, where they have an incentive to move toward you, and even then, requiring your opponent to do most of the work/setup. It does have the advantage of letting you hit-confirm it ("Did I hit the very end? Let me rest after this F-Air" vs. "Oh, I didn't get it late enough; let's just go for general pressure after F-Air"), though, which is something. I realize you said you have to hit with the very end of it, but it shouldn't be understated how situational this is.
In other news, I'm pretty sure D-Air -> double-jump Rest is a reliable way to land it at percents where it would KO afterward (25-40% range before the D-Air, depending on character). What I've been doing/need to practice is getting them caught in it early (can be used out-of-shield on some moves/characters and is a solid spacing tool), drifting away so that you guarantee they get popped forward at the end, then drifting forward near the last night. This allows you to already be at full air speed when they fly away, which allows you to catch up with them in a way that starting to move forward right at the final hit does not.