I could see how a 1v1 mode, while there are many who complain for bigger modes than the 4v4 already confirmed, would be very smart because it ensures similar success to the system of PvP that Blade and Soul is an esport over--having 2 modes one 1v1, the other tag team 3v3.
Overall I'm excited for this game and hope we learn a lot more about it (and hopefully a release date) at E3 2016.