Another point to consider is resale value. Unlocked devices hold their value way better than carrier flagships do. I have owned almost every flagship over the last 2 years and I take a bigger hit on them then I do unlocked devices when I sell them on Swappa. You could buy the Oneplus now and probably still sell it for $250-$300 when the Two is released and buy that if you feel the need.
If you are in to roms, community support and a very customizable device then the Oneplus is a great choice. I just can't see paying $600-$900 for another "Flagship" device when the Oneplus is just as good or even better for $363 with shipping!