This PvP idea sound intresting. I just thought few ideas that could be fun.
There could be adventure where both parties have different goals, other one would try to defence some object and other would try attack it. And it would be even more intresting if there could be example 4 vs 4 play or something...
One could be something like speed race. The first to destroy head camp would be winner but players could also attack the other party.
And then there is pure dominate whole island, different sections u would have to first take for yourself and then try to conquer other sections. One who conquers them all would be winner.
Please comment these ideas, what do think?