I have no special knowledge of canon hardware, but not everything can be done in software on special purpose chips. There may not be the necessay capabilities on the chip to display what you need.  I agree, it would be nice.  I shot a number of exposures of very red roses and learned, as you did, that you can be completely out of range on the red and never know it.  Makes me much more gun shy about moving to right.

I know this topic has been covered previously, but my recent experiences trouble me still.

It seems to me that a firmware update from Canon could solve one or both of the following problems: providing a histogram based on interpolated color data (in some assumed space) rather than raw sensor data; and providing per-channel histograms in info mode.

So, why won't Canon provide such a firmware upgrade?  I feel abandoned by Canon since they seem to be applying the hardware model to their firmware.  Why don't thy even license this code to third parties so they can continue to support discontinued products?

I have had this problem as well. Lately I have taken an "expose to the right minus a 1/2 stop" approach. I convert the RAW to 16-bit. It seems to be working out, but I am far from experienced.