Sasuke,Itatchi, and Kakashi all seemed to use their sharingan differently just like Hinata and Neji's byakugun. So i was thinking that after you have mastered your sharingan (4 stacks) you can go back and pretty much reset again into one of three versions of the sharingan. If you choose kakashi's you can get that jutsu he does with his sharingan ( never found out the name). If you choose Sasuke you get an even greater dodging ability ( enemies get even weaker). If you choose Itatchi's you'll get that third jutsu he learns (starts with an S...) You keep your original Sharingan techniques, except each type is different. Kakashi's version would need double the chakra. So to activate 3 tomoe sharingan it's 2 chakra. To activate mangekyou it's 6 chakra and to use his explosive dimension jutsu it's 20. Sasuke on the other hand will just have normal mangekyou abilities but with improved dodging and riposting skills. Now Itatchi's jutsu i'm not exactly sure what it does but it seems to be like a giant fire demon he summons and pretty much destroys the whole place. So he would have that ability in additon to the other mangekyou jutsu. I was also thinking that maybe it could do with alignment. Good=kakashi, Lawful Evil= Sasuke, Chaotic Evil= Itatchi. Then i was thinking maybe you could just choose and then once you master all three you can reset to have all the abilites but that's a bit overpowered.
For the Byakagun i haven't exactly kept up that much with the manga so.. anyways i thought i remembered from somewhere kaiten can't be learned but by the most talented Hyuuga 0_o i think. So i think that should be neji's ability. Jyuuken, 64 palms and the weakening of enemies are the normal abilities learned. So anyways Neji would have kaiten, Hinata would have her Protective Palms ( the thing where she makes sharp chakra and uses it as a shield+ a weapon. This could maybe go with alignment... eh maybe.. >_> hinata= lawful good, neji= chaotic, good (what goes with evil??)
The kaguya clan only had one survivor... and the gates are pretty much the same for lee + guy. Anyways the point was kinda to give people more to do... >_>