When it comes to the future of Cree bins, you have to take into account the amount of difference/gain in lumens between each bin. Let's take a look at the Cree bin guide:
So we're currently at Q5 (and in a few rare instances, R2) and the chart shows what we can expect in the future all the way out to the R4 bins. What's the final net difference for the flashlight user? We know the Fenix L0D, for example, uses the Q4 emitter and is rated at 75 lumens, so what if we dropped a Q5 into it? According to the chart, the difference between the Q4 and Q5 bins is right around 7%, so extrapolating from that (7% over 75 lumens) the finshed L0D Q5 would put out 80 lumens, or five lumens more than the Q4.
"Is that good?" Well not really, and here's why - the human perception of light is
logarithmic; meaning that as the pupils of your eyes adjust to a brighter light, it requires a greater leap in lumens for you to perceive a difference. Generally speaking, a light must be about 20% brighter than what you're comparing it to before you even notice a change. That means our new and improved L0D would have to put out at least 90 lumens to even marginally distinguish it from the current model.
What if we took it to the extreme and went into the future to acquire a prototype R4 emitter for our L0D? Again going by the chart numbers, the R4 is 30% brighter than the Q4, which would give you a grand total of 98 lumens - just barely enough of an output increase to note a difference. (By comparison, most people complain that the Medium and High output levels on the P1D are too close together - yet the High mode is nearly 90% brighter!)