I’m wondering how horrendous it would be to include parsing of popular trajectory files, so I had a look at how MDTraj did it with (e.g.) the xtc format. A layer of python, then cython and then a set of c files adapted from gromacs.
Yes I think Chemfiles.jl is the way to do this in Julia at the minute. It wraps the chemfiles C++ library.
It should be possible to write pure Julia parsers as well, and they should be able to achieve similar speeds to C++. Personally I have no plans to add such parsers to BioStructures.jl due to time constraints.