Understand that you can make OLEDs last longer by making more blue pixels or bigger blue pixels and then running the color blue with less intensity translating to the same net effect. For example 2 blue pixels at 4 lumens produces the same amount as blue as 1 blue pixel
The downside is that if the pixels are to large our eye notices especially the blue wavelengths are the most sensitive of all the color wavelengths.
That said the technology of oled is rapidly fixing that problems (smaller geometries) and the technology can still grow.At the same time there are mechanical limits with LCD technologies so eventually that technology will level off in the upcoming years or even a decade.
You can also have a white subpixel which has many of the same advantages and disadvantages as more blue subpixels. The moto x2 a 2011 rgbw oled phone had a brightness that was the highest in 2011 of 697 nits
http://images.anandtech.com/graphs/graph4483/39397.png
Now compare that to 2014 devices
http://www.anandtech.com/bench/PhoneTablet14/986
Samsung's s5 has a brightness of 352.7 and the iphone6 is 559.3
Now brightness is not everything how the glass is designed matters for the more reflections the less viewable an image is in sunlight. Now matte images may cut down on reflections but it also modifies the light by the same effect and sometimes the picture looks grainy as a consequence.