Thanks for the idea!
We are unlikely to implement this idea at this time. As Jira does not support attachments on custom fields yet, the workaround is what you mentioned to add attachments to the main description attachment area. One suggestion would be to submit a request to Jira to improve this functionality so you can tie your attachments to the correct fields in Jira.
We will continue to monitor this idea for community feedback. We hope you can understand.