The practical problem I have with a C2 jump putt rule is that eyeballing and walking off C2 is FAR tougher than walking off C1. For DGPT this isn't an issue, they mark it off with flags, but for other events it could be a huge issue. Right now I can fairly easily walk off my 13 paces which I know is roughly C1, double that to 26 paces and I am willing to bet the inaccuracy gets out of hand.
Imagine getting the obligatory "Am I outside?" question on an unmarked green and having to make the call on whether you are inside our outside of C2. It is sometimes tough enough with C1, can't even imagine C2.
C1 rules are not designed on rough estimates to start with. If we are already estimating this distance for a rule, I am confused on the issue of further "graying" of the rule.