Since we are doing "could have" abilities this is going to be different.
Technically, if Suigetsu develops the skills of the Seven Ninja Swordsmen and his clansmen Gengetsu, as I believe he should, then he would still lose badly to Naruto.
Unlikely other sensors, Naruto has the ability to sense negative emotion, which means Naruto will be able to sense Suigetsu regardless of whether the latter is using genjutsu or mist to hide himself. Also, Naruto is capable of flight, which makes it much more difficult to fight him. Lastly, Naruto has access to Tailed Beast Balls, which are confirmed to be able to knock Suigetsu out.
It still remains to be seen if Suigetsu can be "killed" or not, however. Even with all of his chakra, Naruto might need to find a way to kill him, which means Naruto might just imprison Suigetsu in a glass container like Orochimaru did, and then do research on how to kill him.
Otherwie, their battle is pretty cut and dry, Naruto is an exceptionally powerful shinobi, probably easily in the Top 5. Suigetsu will be luckly to just be considered Kage-level. So the power difference between them is too great.
Hey I'm not sure if I asked you this already but where did you get that pic of naruto and sasuke, with all the tailed beast? I asked you or omega64 once and had it but someone deleted it off my sd card and I can't find it in your conversation anymore