Distro does packaging of programs, program's documentation comes from upstream.
If somebody wants to keep statistics on maturity and level of documentation of these upstream projects that distro packages, I guess distro could provide some infrastructure for users for that. I'm not really sure what value that would provide or who would be interested to maintain it though.
The levels you proposed were way too vague. Distro having e.g. 90 programs at level 3 doesn't really tell anything. If I would be interested about some specific program, I would want to know what specific features it has, how well its UI and documentation is translated, has it fixed my pet peeves from earlier versions etc. things that e.g. Ubuntu's Launchpad collects.