OK, I understand now that there is no plan to support relax-ng at the moment.
The current issue that I have during conversion was the output of `xsltproc xsd2rng tsd.xsd` is not a valid rng. The author of xsd2rng does claim that it is not able to convert all xsd perfectly. https://github.com/epiasini/XSDtoRNG
There are two ways that I think to get a rng version:
1. Fix xsd2rng.
2. Fork xsd-generator (github.com/NativeScript/xsd-generator.git) to support for spiting out relax-ng
I won't be working on it, but I appreciate if someone does.