It is interesting that you brought this up because I was in the lab with this very recently. I used Falcon as my test subject, and starting at about 10% the following appear to be true combos.
1. Auto-cancelled QD --> D-tilt --> U-tilt
The stronger hit of U-tilt almost always hits. If it does not, then the lingering hit will.
2. Auto-cancelled QD --> D-tilt --> B-air --> Grab --> D-throw/U-throw --> Any aerial, except D-air.
The momentum from QD will allow you to slide a bit past your opponent while using D-tilt. This puts you in a perfect position to use B-air afterward, then do a turnaround Grab.
Some other things I know that makes use of QD's momentum:
- Sliding Eruption
- Turnaround B-air (looks like RAR B-air, but no dashing involved)
QD as an offensive tool is a commitment, but it can be useful against those that are unaware of its cancel properties. I may plan on dedicating a video to this soon. ^-^