ok. let me first say that this is mostly speculation. tl:dr at the bottom
I,ve been trying to think of a way for alot of things to make sense. now that we have seen sasuke tho and itachi fighting someone who well represented a person relying on yang styled jutsu. much like naruto does kabuto fight, abet, as ive said in a more modern version( cell and kekkei genkai) but also not ignoring older methods (sage mode, uzamaki). if he gets sasuke he will very well gain alot of power. this can be expected considering how much we have seen other characters ( madara, tobi, nagato, basically anyone related to so6p) sharing abilities and gaining power.
but wait. itachi is with him, and if anything should be apparent itachi is an edo... his spirit is in the real world attached to a body.
rewind. minato sacrificed his soul and kushina bound some of her soul to naruto. what is to prevent itachi using an ability to bind his soul to sasuke. maybe even with a uchiha ability. uchiha senju and uzamaki are related and despite different methods they all have similarities when approaching the same power levels.
in effect sasuke could gain more from the brother that loved him. his spirit.
more spiritually influenced.
itachi still present in the real world, threw sasuke.
itachi able to communicate with sasuke
a route for sasuke to be saved from darkness.
he wouldnt want to accept power from his brother any more than he has?
If you can think of cons then go ahead and post. post about your interpretations of what ive said, i know i can be alittle off. (TLR)but sasuke wont be a match against people like kabuto and naruto if he doesnt power up more than we have seen. he has taken from itachi before, why not again? and what are the implications?