Thanks for asking... I have my own theory about the development of the
Sharingan, if you have read the the whole manga or saw the anime from episode 1 to the the fight between Naruto and Sasuke and you noticed the evolution of the sharingan in
Sasuke's eyes. I posted a theory at Manga Helpers about the Sharingan based in true facts. I'll sumarize it here.
The Magenkyo Sharingan don't requiere killing your bets friend.- 1st Tomoe: Sasuke obtained the sharingan with one tomoe, when he was trying very hard to see haku's movements, after that he suddenly woke up the sharingan with 3 tomoe in total, one the eye of the left and 2 in the eye of the right.
- The 2nd tomoe: He woke up the second tomoe of his right eye when was fighting against lee, Sasuke said: this gives me a chance to practice it.
- The third tomoe: This one appeared at the valley of the end, just right after sasuke used the cursed seal to see naruto's movement, at that point he woke the third tomoe.
My Magenkyo Sharingan theory(tm)
Itachi said that if you want to obtain magenkyo sharingan then you'll have to kill your best friend, but that's not true... because
Kakashi didn't kill
Obito in order to get
Magenkyo Sharingan. The true is that
Itachi and Kakashi both obtained the
Magenkyo Sharingan with their intense experience in batttle, just like Sasuke completed his 3rd tomoe. If you look at ch363 sasuke used a time-space teleportation jutsu, just like one of Kakashi's
Magenkyo Sharingan effects, he used something similar against deidara, in otherd words...
Sasuke is awakening his
Magenkyo Sharingan.
Some people says that Kakashi felt so bad about Obito's dead to the point of feeling guilty of his dead. But that would go against the breaking bonds theory said by
Itachi.