Sounds like a good idea!
My interest is mainly in category 1, and particularly in getting molecular simulation to work with automatic differentiation tools.
Another interesting topic to discuss would be how best to develop packages for algorithms used in a variety of chemical contexts, such as long-range electrostatics (Electrostatics in Julia).
reading/writing these representations to common file types
There is GitHub - chemfiles/Chemfiles.jl: Julia bindings to chemfiles which goes in this direction.