Yoshi already talked about open world PvP sometime around end of Stormblood. He said the devs could already just tag an area for PvP but they haven't done that in the live game cause there aren't enough people looking for that kind of content. Only 1/3 of the current PvP modes are active for 6-7 hours a day and rest of the modes only happen during ranked seasons/community events. Splitting the small PvP community into even more modes might be bad for all of the modes. Now it would be important that the new small scale PvP mode is a success because that would help with the problem that the only PvP happening actively is Frontline that requires 72 players that has no chance for it to pop before the daily reset.