You can't control when it happens out of shield because your opponent is moving all around your shield and a reverse up B won't always result in this effect. Go ahead, try it in your next match.
You need SDI to escape Fox's uthrow uair, at a precise timing, at a precise direction. For this, you literally just have to hold a single direction to avoid the spiking hitbox, anywhere that isn't into the hitbox. It's far easier than most other DI requirements in the game because of how much time you have to input the DI and the nonspecificity of the DI direction. You can be pressuring my shield and then react to getting hit by my up B and easily have plenty of time to move the control stick away. It's not that it's escapable, it's that it's very easily escapable. Let's turn this around. Your jab cancel pressure Fox's shield, and Fox manages to grab you, and instantly dthrow dsmashes. Do you get hit by it? Of course not, dthrow to dsmash is ridiculously easy to avoid, not only can you tech, but you can DI away. Foxes usually dthrow->tech chase because Samus's tech roll is slower than Fox's dash. This is very similar to this technique. They can DI away to avoid being spiked, and even if they are spiked, they can tech the ground before Samus can do anything to follow up. There's no reason to do it, it's counter productive to the reason you want to Up B out of shield in the first place, to gain frame advantage or a combo. When you hit a normal up B out of shield to a top platform, you want your opponent to land on the top platform or on the side platform, because now you make the first action. It's not productive to have them hurtling downward toward the side platform rapidly, because they can just tech and now you don't have the first action, they do.
then it forces them into the air, away from you, and possibly off stage.
All these things are not necessarily good if they don't get you frame advantage. When you up B a Fox at low percents on Final Destination, and you don't have a good landing in mind, like the edge, they get to spam laser until they laser cancel their landing out of tumble rather than hitting the ground and entering knockdown. Your up B forced them into the air and away from you, and possibly off stage, but because they get to touch the ground while not in knockdown first, they have frame advantage, and that's why up Bing in that situation is bad. Similarly, if you up B and happen to hit a reverse spike, now they're either on the ground even faster than before, or slightly off stage, while you can't follow up. They double jump back on stage, and now you've finally landed, and they're running before you get out of special landing lag.
Again, I fail to see the uses.
You send your opponent to the ground faster, which is bad.
You can't follow up on it, which is bad.
You give your opponent frame advantage, which is bad.
So yeah. Not new, not consistently usable, and not a desirable outcome.