ok i read your theory several times, and while it would be cool i jst dnt see how its possible. first off how was e released from the reaper death seal? 2, how exactly did he travel back in time? 3, say all this is true, say minato did go back in time and is now tobi trying to stop madara from ending the world or something, why not just kill kabuto? kabuto, who brought madara back, or better yet why not time travel to the fight between hashirama and madara and team up with hashirama to end madara completely? u say he was trying to make naruto stronger, and while this is a valid thought, it just doesnt make sense why someone powerful enough to travel back in time, capture several biju, steal a sharingan, give someone a rinnegan, and is also smart enough to form such an elaborate plan, take the risk of having his son grow up to maybe be strong enough to take out arguably the strongest ninja ever instead of just killing kabuto from the start and stopping the whole fiasco?
But i like the idea