He wants the whole package, not just the eyes. If he just wanted the eyes he could have gotten those forever ago instead of implanting them into Danzo's arm. With the Uchiha kekkei genkai, he'll be able to use the sharingan with almost no side effects and still have the potential to advance it, or deactivate it as he sees fit (unlike Kakashi who has to keep it covered). On top of this the Uchiha have strong bodies as well as large chakra reserves. He would finally be able to master dragon sage mode and he'd have all of Sasuke's sharingan abilities. He'd probably be unbeatable.
