Hypothetical personal favorite endings for Boruto made by me.
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-The ghost of the Uchiha-
Orochimaru goes completely unstable and decides the Otsotsuki threat was too much of a hassle, therefore he burns down the current world order.
Since Madaras body is most likely decently preserved, Orochimaru uses Edo Tensei to reanimate Madara. Madara breaks the reanimation jutsu to gain an immortal body with infinite chakra, then summos the Gedo statue.
Madara hunts down all the tailed beasts, extracts their chakra, and is only left with one, Kurama. As we've seen in the war arc of Naruto Shippuen, the Gedo statue doesnt require the full tailed beasts chakra in order to summon the Ten-Tails, rather only requires a tiny fraction of the chakra. (In the war arc, Madara and Obito used the Nine-Tails chakra from Kinkaku and Ginkaku in order to summon the ten tails), meaning, Madara could extract Himawari's Nine-Tails chakra, and resummons the Ten-Tails
Since no one in the verse has the Six Paths Yin-Yang seals required to stop his Limbo clones or seal him away, he is basically unstoppable. And because Black Zetsu and Kaguya are sealed away, he successfully casts the Infinite Tsukuyomi, puts the Otsutsuki and to sleep, and the Shinobi era ends on his terms.
-The Last-
After Boruto manages to defeat Hidari and free Sasuke from the Divine Tree trunk, Sasuke’s body is severely weakened, missing his left arm and his rinnesharingan. Knowing he needs a massive power up to face the Otsutsuki and Shinju threats, Sasuke tracks down the preserved body of Madara.
He implants Madara’s straight tomoe Mangekyo Sharingan into his empty eye socket and grafts the Hashirama cells directly from Madara’s chest onto his missing arm.
This triggers the ultimate synergy, the pure Senju cells instantly regenerate his dominant left arm, giving him his full physical combat capabilities back.
The Hashirama cells grant him near bottomless chakra reserves, completely erasing his biggest weakness from the sequel series.
By taking Madara's eye data, Sasuke inherits Madara's specific ability, Limbo.
In the current meta, no one has the Six Paths Yin-Yang seals required to seal Limbo clones away. Since Otsutsuki and Karma users rely heavily on absorbing chakra attacks, they have a massive blind spot against physical, invisible clones attacking from another dimension. Sasuke uses the peak of Shinobi history to single handedly clear the verse, proving that the "Last" Uchiha is the greatest to ever live.