This does not solve the problem of different dumping period. If I dump ions every 5th and electrons every 100 steps and I will analyse only electrons it is more complex to write a post processing skript. In the future it became more complex if we had more than 2 species.
The same is if I will check which groups are in my hdf5 files, it is not possible to check only the first file and dump all names (e.g. with plsh2txt), you must first scan all files to be sure that you found all groups.