Hello, I've come to get my two cents. 

The gist of Mirai Nikki was less about knowing the future and more of changing it. To make this a successful non-broken pvp RP(and Mirai Nikki should definitely be pvp), you should simply impose some rules and conditions. Some rules and stuff should be this;

#1. Players should be allowed to change any the future as long as it is related to their diary. If person 1 says person 3 will be on X location on X day, then person 3 should NOT change that future unless his diary type gives him information that would make him do otherwise.

#2. Players need to align entries. If player 1 made an entry saying playing 3 will be at X location on X day, player 2 shouldn't make the exact same entry saying player 3 is elsewhere on X location on X day.

#3. Realism and fun. Your character should only know what he/she knows. *hinting at abusing other player's entries*. There is no 1 million dollar prize if you win this RP. There is no need to ruin other people's fun so you can win and theres sure as hell no way being a dick/powerplayer will make your win satisfying. 

#4. Players are randomly given X number of chances by GM to inflict DEAD ENDS on others, this will make the game creative. If you're cornered by a legitimate DEAD END and scenario where changing the future is no longer possible, players should then die gracefully <3