More random match-up knowledge:
Something you'll see characters like Sheik, Marth, Falcon, and space animals do sometimes against Falco is jump into his dair at low percentages, land, and punish him. Sheik, Marth, and Falcon are tall and get a decent frame advantage because of that; space animals get less of an advantage, but they have a frame 1 move that compensates for that.
ICs are short, and if Falco dairs (with the strong hitbox, which I'll assume throughout this post) both of them at the same time, ICs typically don't get that much of an advantage. I generally observed around 5 frames, which is only enough time to jab, which is often unsafe against ASDI down -> shine. However, if Falco hits both ICs at different times, he can experience substantially more hitlag, which can yield a much bigger advantage. In particular, let's look at the following picture:
In this picture, Popo just jumped and Nana is in jumpsquat, during which she crouches a bit before jumping. If Falco falls on Popo with dair around this position and hits Nana a bit later, he'll experience quite a bit of hitlag, and ICs will generally be able to act around 10-13 frames before Falco will. This is a comfortable amount of time to get a grab off of which you might be able to kill Falco.
Considering that ICs already have pretty good options for beating a lot of dairs, it's worth looking at how this compares to the alternatives. Utilt is fast, and gets a good reward if you can connect with the last hit,but it's becoming less relevant in the ICs metagame as people get better at SDIing out of it, and it also is somewhat limited in that you need to commit to a position on the ground to do it, and you can't do it OoS. AC uair is nice, and perfectly done only comes out a frame later than utilt does, but can still be somewhat difficult to do on reaction, partially since you rise a bit off the ground, meaning Falco will reach you a tiny bit faster than if you stayed on the ground. Usmash is great if it hits at low percentages, and will often lead to a grab or at a least good combo, but it's not active that long, takes a while to come out, and is quite punishable afterwards.
The big downsides to jumping into a dair like this are that you take damage and that it doesn't work past a certain point. It looked like it worked up to 37% when I was testing it yesterday. Another downside is that it's unsafe if Falco chooses to nair or bair. However, it can get you a grab, which kills more reliably than the alternatives, so I think it's an option worth having in mind.