How would killing the kages and trapping the TB create a "clean slate". It would just start another war and more fighting.
And I seriously doubt Sasuke, who has never killed anyone before, would murder the kages one by one in their sleep.
Also, this is a kids show so that will never happen. Grammar.
Without the Current Kage, the entire Ninja World will be forced to change, as the Villages can't function properly without the head shinobi (Kage) in charge to attend to the tasks necessary to run a village. Without access to Tailed Beasts, no Village will have an edge over the other, and as such won't be able to threaten other villages (i.e. "Provide us with intel/kekkai genkai/rare ninja items or we'll send over our tailed beast to destroy your village.") Keep in mind that the purpose of this current war was
to obtain the remaining tailed beasts. While 'Clean Slate' may not be entirely accurate, such drastic changes would no doubt impact the shinobi world
greatly.
Although those who fell victim to him weren't more than support characters (or even less), Sasuke has
indeed killed before, and does possess the drive required to kill. During the Summit, he mercilessly cut down dozens of Samurai without the slightest hesistation. He left Karin for dead after piercing her to fatally wound Danzo, and would've killed the latter had he not taken his own life with his sealing jutsu in a last-ditch effort to get rid of Sasuke and Tobi/Obito. He attempted to kill Sakura
twice, and would have done so had it not been for Kakashi and Naruto's interventions (Plot Armor). In the manga, upon Obito and Madara's defeat, he was the first to rush in and kill them for their actions, only to be stopped once again (Plot Armor). Since the destruction of his clan his life has revolved around the very concept of hatred. The most obvious display of this is his development of Susano'o which grew more potent the more his hatred deepened. It's more that something always interferes with the act of killing than him not possessing the ability to do so. So it would be in your best interest to take him at his word when he declared his true intentions. If he's left unchecked by Naruto, he
will kill off the Kage.
"This is a kid's show so that would never happen" is an extremely weak excuse. There have had to have been hundreds of deaths in the Naruto Series at this point, most of which were shown in the Anime/Manga, and some of which were particularly gruesome/unsettling, so that means nothing.
