My main question in regards to this is: Where would this actually be happening? For the most part FF14 has extremely few reasons for players to actually be battling in the overworld unless they're done with the game. MSQ is almost entirely cutscenes, and if you're grinding FATEs you're probably grinding a secondary job, so people PvPing in the overworld would either not care, or be annoyed as they're griefed by higher level chars (or on the other side: higher levels who're trolling).

I could see this being implemented in a "grind zone" similar to eureka/bozja though, maybe with the multi-faction aspect of Dawntrail as part of it. But I doubt we'd see it as a general thing.