We are interested in extending Wireshark's GUI support for adding pcap-ng comments to editcap. It seems like editcap is a logical place for this type of functionality. This would allow other tools to modify the comment field of pcap-ng files. We envisioned a simple command-line interface that would allow multiple comments to be specified on the command-line as well as a specifying a file name for bulk comments.
We've done a proof of concept and submitted a patch file under this bugzilla ticket.
Regards,
--joe