I looked over libconf and it seems like a good library that I don't mind having as an optional dependency for yt. In particular, it's:
* Reasonably up-to-date and maintained (last release early this year)
* Pure python, supporting python 2 and 3, with a universal wheel available on pypi
* Permissively licensed.
While it would be nice if we could do this without adding a new dependency, if pyparselibconfig isn't sufficient, and Britton doesn't want to work on fixing it, I think the suggested approach is fine (unless someone steps up to fix pyparselibconfig).
If we do decide to go this route, I'd prefer it if we remove pyparselibconfig and drop support in the Enzo frontend for libconfig parameter files in enzo-3.0. In the real world, I don't think many (any?) datasets were produced using that format, since the PR adding support for it was never merged, and I'd prefer we don't have known-buggy code in the codebase to trip up any possible future users.