A couple of weeks back we released a beta for nbconvert 5.0 equipped with XeLaTeX, internal use of entrypoints to find exporters, an AsciiDoc exporter, and a html sanitisation preprocessor (along with a number of other internal fixes and documentation improvements).
Get the beta by including the `--pre` flag when you pip install.
Feedback on the updated version is welcome either here or on GitHub.
Cheers,
Mike