This library provides great functionality for TestNG tests. Could you provide same functionality for JUnit tests? Because there is no similar experienced project likes yours.
You can, if I recall correctly, run JUnit tests using TestNG, which would be one way to use ReportNG with JUnit tests.
As for developing something that works directly with JUnit, that's not something that would be worthwhile for me personally since I don't use JUnit. If somebody else wants to reuse parts of ReportNG for a JUnit solution then they are welcome to do so, but I'm not sure how useful it would be as ReportNG is quite tightly tied to TestNG and its classes. It doesn't have any nicely decoupled design, it was just hacked together to scratch an itch.