Simply more diodes could certainly achieve that end, whereas you could turn some off, and turn others on... Depending on developmental cycle.
Having a diode that could do it on they fly would be most ideal.
I think the substrate that they use for the diodes themselves is a limiting factor. Once the composition is created, It's static, (fixed light spectrum) and it would have to somehow become dynamic, or perhaps you would need to filter it somehow, and that would greatly diminish it's efficiency.
Maybe one day they will be able to control something like that with electrical input somehow, but that's far beyond anything I can imagine happening.
Certainly different ratio's could be obtained by adding a small circut brain, then simply an array of various spectrum diodes to control the outputs.
Big dollars...
Personally, I see that there seems to be some standardization that's occurring, especially with the strips. If that continues, people will essentially be able to custom build anything they want, eventually. You really already can, but for the novice, I mean. Sure would be nice if you could rebuild, or update your units for less than buying a new light. I suppose this is wishful thinking on my part.
That's what I want to see happen the most, is more universal ways of doing things. Interchangeability. (like computers) Standardize the strips, the diodes for goodness sake. So things can be easily serviced.