The only problem i see with that is that it requires a read. Samus's usmash is a pretty slow move to cover the span of the upsmash. If falco baits it, its an easy punish. It doesn really have any fast startup or ending animations so it can be baited and punished rather easily. Now if you do get it, it can be a good mixup but the problem lies within the hitboxes and the percentage the opponent is at. You can get the weak hitboxes at the beggining and you still need to complete the animation and falco just falls our for another punish if they're good at reacting. And if you you manage to finish the animation, there isnt really any good Knockback on the move so you're still within Falco's close range that he can react to what you do.
I think you would have to rely on getting the back good hitbox of it and landing that is somewhat unreliable.
I may be recalling the knockback and the speed of upsmash wrong but this is me theorycrafting based on my recollection of the move. It may work as a mixup just to stop dairs every once in a while but I wouldn't rely in it heavily to turn the tides in Falco's favor.
Maybe someone else has some insight on this?