This is ATT-4 but this ticket is already being worked on, and will be completed soon.
Looking at the pending issues, quite a few of them are rather UI-related.
However in term of REST support there would be two things to do that have not been framed by actual tickets:
- Enable the ‘generic file upload’ feature. See my response on this thread here.
AttachmentResource to return lists of attachments based on a query parameter.
I would rather have you start with the latter for now. Is that something you’d be interested to spike at?