Inspired by a 1-off comment in Psyckosama's rewrite of Making Uzumaki.
Idea: Sasuke seeks out the cultists of Jashin and has them perform the same secret techniques they used on Hidan, thinking that immortality would help him against Itachi.
Bonus points if he seeks them out either during or immediately after part 1, and a side effect of the techniques is that his ageing is arrested.