What I want to see before the end of the series:
- Another element that he could use to expand his arsenal (Most likely Water or Fire) and possibly make a fire based Rasengan.
- Possibly a couple of sealing techniques since he is an Uzumaki and all...
- Now don't flame me on this one: I want him to get the Rinnegan.
With 2 elements (Assuming he actually uses Wind for something else other than FRS), a couple of sealing techs and the Rinnegan, Naruto is arguably (oh who am I kidding)... THE STRONGEST IN THE SERIES.
To compensate on Sasuke's side: He gets the Elder Son Dojutsu (Power's unknown but presumably powerful and it would be on top of his EMS tech's) and Perfect Stabilized Susanoo.
It's pretty clear by the end they will be the strongest, so why not go all in