While I in general agree that any new format introduced needs to be carefully weighed against the upheaval it causes, it appears the RVZ format has gained much traction and continues to grow. I'm no programmer, but I do understand you have to balance the time cost/benefit of adding something like this. In this case, if it's not too in-depth beyond adding the compression profile, I think it would be invaluable. Here's a quote I found from someone scratching the surface of the problems with CHD:
"MAME is sometimes so disappointing, they create the only cd image format that has delta encoding, then they do absolutely nothing to make it easy to use with the current state of the world (which for romhacks in particular is xdelta patches on the binary track). They're even considering 'reworking' chd to a 'more accurate' format - to be clear, this probably would require redumps of absolutely everything, and i can think of no finer way to kill the format."
..and finally, a hearty thanks for the years of effort on this software. It is greatly appreciated!