Sarada Versus: A Meditation on her Mangekyo Sharingan
Sarada's new ability could spell bad news Kawaki, Code, and others.

In the last pages of Boruto: Two Blue Vortex's chapter 20, readers received their first peak at Sarada's Mangekyo Sharingan (MS) abilities for the first time, tempting us with just a taste in the closing pages.
What is Sarada's MS ability?
The short answer? We don't know yet.
Sarada's Sharingan activates. She drops her kunai and closes her eyes. Shinki's iron sand lifts off of her, off of Mitsuki, off of Ryu himself, getting drawn into a swirling vortex above the battlefield. When Sarada opens her eyes, she stares straight ahead, then looks at Mitsuki, her MS activated.
I'm going to propose three possibilities for what her power actually is, then review how it could counter the abilities of other characters in the universe.
Black Hole
The most popular theory, and the one I lean towards, is that Sarada's MS creates a black hole hole, drawing things into it. It appears to be selective, as only Ryu's iron sand is attracted to it at this point, the sand on the ground unaffected. Sarada's MS pattern being a sun and a it's ability being a black hole (a collapsed sun) fit well with the interstellar themes depicted in Boruto.
(A sister theory to this one is that the other side of her black hole ability is connected to another dimension.)
Magnetism
Another possibility that arises from Shinki's iron sand being first targeted is that Sarada can manipulate magnetic fields (and gravity itself is a magnetic force). This could be the reason why she drops her kunai before activating it. The effect itself could still be building, thus attracting the most light-weight metal components into it before its strength affects others.
(Side note: This could end up linking to Boruto's Flying Raijin working with metal markers.)
Stealing Abilities
While we see the iron sand gathering in the sky, we still don't know what happens next. Does it get sucked away? Compressed into a solid ball? Or, is Sarada able to utilize Ryu's power herself?
Each of those possibilities have different consequences when it comes to combat with particular characters.
Sukunahikona vs Sharingan
The Boruto narrative has long drawn parallels between Sarada and Kawaki, two characters both drawn to Naruto's warmth and familial approach to the village. Through Naruto, Sarada is inspired to become Hokage, a shinobi capable of protecting others. Conversely, Kawaki wants to protect Naruto instead of emulating him by extending that love to others.
If Sarada's MS manifests as a miniature black hole, she'd be a formidable foe for Kawaki's Sukunahikona. As we see in the fight with Ryu, small particles are immediately drawn to it, which would counter Kawaki's ability to shrink objects (such as the cubes, columns, and black rods) and hide them around him, enlarging them later. Any miniaturized matter, including Kawaki himself, would get sucked into Sarada's MS vortex.
What makes this especially dangerous is that Sarada doesn't look at the "black hole" while it's absorbing small particles, leaving her open to use both taijutsu and genjutsu in a one-on-one battle against Kawaki, not to mention her Susanoo. While karma has granted Kawaki thousands of years of battle knowledge, we know from the manga that Sarada is able to use here Sharingan to watch her opponent's abilities and mirror them, as she did in her training session with her mother. While it's very likely she'd be out-matched by Kawaki's Otsutsuki-enhanced strength, she'll be able to use genjutsu to get the upper hand.
Code vs Magnetism
What does Ryu's sand and Code's claw marks have in common? That's right: tiny amounts of iron. While Code's shinjutsu transportation portals are primarily chakra-based, he infuses them with iron from his blood so they can't be absorbed through Karma. That's a neat trick until you have a character enter the story to draw metals towards her.
The Claw Grimes and Shinju are also made up of the same belts as Code's claw marks, infused with amounts of iron from his blood. Would it be possible for Sarada to remove the blood-infused belts from the Claw Grimes that created them in the first place, releasing the chakra that made them useful? Similarly, could she remove the iron that's essential to the Shinju, the part of himself that Code gave them, accidentally bringing them to life.
(I'd also be remiss if I didn't add here that if magnetism extended to gravity as well, Kawaki might have a little more difficulty than usual flying. Speaking of Kawaki... Are the scientific ninja tools in his body organic or is he also enhanced by metal through Amado's experiments?)
Return of the Copy-nin
The possibility that Sarada's MS could help her steal the abilities of others is a tantalizing proposition, one that could enhance her power to equal any foe she faces. While this might seem to be a power more suitable for the previous generation of shinobi, rife with kekkei genkai, the real question is: Exactly what can she steal? How much can she steal And what happens to the person she stole it from?
A Sarada who can just take the abilities of another ninja would be woefully under-powered when compared to the threats facing the modern Shinobi world. However, if she could combine the powers of others, Biju strength, Shinjutsu, or even Karma itself, she'd be a threat to be reckoned with. Even more tantalizing: What happens to the person she takes the abilities from? Could this be key to saving Boruto from Momoshiki within him? But what would be the cost to Sarada of taking on those powers herself?
Conclusion
While this was just supposed to be a meditation on Sarada vs Kawaki, the more I looked at the last panels from chapter 20, the less certain I was of what her ability would actually do. We're going to be left hanging until next month, so all we can do in the meantime is speculate and have fun with the what-ifs of Sarada's MS.