I honestly see Naruto being the one who awakens the Rinnegan, given his parallels with Rikudou and the advent of the Rinnegan coming from the Bijuu's. But I agree with the rest. I'd rather Sasuke delve deeper in to his clans personal powers (like EMS granting no loss of sight when using Izanagi) and develop Enton on the scale of Hashirama's Mokuton (like creating constructs from the fire like Hashirama did from the wood). A Sasuke with Perfect Susano'o (larger scale), Enton capable of creating constructs like Wood God and Shinsenjuu (think; Enton Tsunami or Enton Tengu) and possibly "Time" Manipulation, and Sasuke is an incredible match-up for a 100% BSM Rinnegan Naruto. It would put Hashirama and Madara's battle to shame.