Could be but it sure seems like something a FW update could alter... I'd like the center red focus in all cases pretty much, not just AI Servo. It's just that I shoot there so much!
I'd still like a RED focus point in AI Servo! +1 on this, too, but I'm guessing there is a hardware limitation that prevented them from including it in the next-to-last firmware update.
be a technical limitation. People who used previous 1-series bodies are used to red AF points. Like other cameras that don't have the transmissive LCD, the AF points are etched into the focus screen, and that makes them easy to illuminate from an angle which avoids significant wide-field reflection. On cameras with a transmissive LCD, there are no etched grooves to 'side-light', but rather the flat surface of the LCD has to be illuminated, and that's a lot less specific. The red light from the illuminator reflects off the surface of the transmissive LCD, and some of it reaches the metering sensor. You can see that here:
That's not a problem for still shooting, but for servo shooting, the near-continuous metering would be impacted by the illumination for the LCD. The solution for the 1D X is intermittent (blinking) illumination of the AF points in servo mode, and although that sounds like it could be implemented on the 5DIII, it's possible that they tweaked the interpretation from the metering sensor to ignore that red light, which might be possible with the RGB metering sensor of the 1D X but not possible with the less distinguishing metering sensor of the 5DIII.
Lots of 'mights' there, and I suppose it's equally likely that Canon simply decided not to add that feature to the 5DIII, just as they decided not to add clean HDMI out to the 1D X.