If we take Kishimoto's word in some interviews around the release of The Last: Naruto the Movie, he most probably had already decided this outcome by 2010. It's not much of a stretch to think that he told CyberConnect2 in strict confidence and then they just ran with it.
- Confirmed. Kishimoto has indeed stated in several post-series interviews (most notably in the 2015 New York Comic Con interview and the 2017 Jump Festa interview, both of which are official translations rather than Fan Translations) that he planned on Naruto/Hinata being the main Official Couple since the early stages of the manga, long before 2010. Kishimoto also stated in this 2013 SaiyanIsland interview that he thinks the Ultimate Ninja Storm video game series is more exciting than the manga, so he prefers these games over the canon that he created.