I think the question is really...what does Itachi plan to do if he gets the mangekyou+1? It's not like it gives him immortality so he'll eventually die, he's young though so I guess he could go on a "I'm so leet!" killing spree on the villages.
Skaw: I didn't mean to say that Kakashi was able to use Mangekyou when he first got the eye and watched Obito die with it, just eventually. Thinking back Obito and Kakashi always hated each other and weren't friends until Rin was kidnapped, but Obito could easily be Kakashi's only friend since Kakashi's attitude wasn't the most stellar
It does make you wonder though, how long has Kakashi been able to use it and why specifically has he used it recently? I know he only uses it in the most dire of dire circumstances, it's probrably because of the 'charge time' to activate it.