Is there some technical reason why reticle illumination could not be done with very small fiber optic inside the scope tube only (no path outside for ambient light to light the fiber) and just use a VERY small efficient LED to light the fiber?

Could it be done in a variable scope?

This seems like the simplest way to get a bright reticle with stupid long battery life, and yet no one has done this yet...am I missing something, or does the ACOG LED work like this?

call a patent attorney

Really though, it sounds like a good doable idea. This is a similar illumination to etched glass illuminated reticles, I believe.

I have seen where people have taped LED keychain lights to their TR-24s, so there is no reason that you can't achieve an LED-illuminated variable that has an internal light source.  However, aren't there some limitations to the reticule designs that one can achieve with FO (at least the way that Trijicon does it)?