Awesome plug-in! Does it work (or can it be enhanced to work) with custom post types? In my case, I want to organize meetings using an events calendar and have meeting materials as attachments to the meeting event... but the event is a CPT and doesn't show the attachments (I'm using Timely All-In-One calendar but I suspect this could be the same for any CPT).
It sounds simple but can you do it?
PS. It might be worth allowing the user to configure which CPTs get auto attachments because other plugins (like the project management plugins out there) already have a way of displaying attachments. Most plugins do not, hence the need for your excellent Auto Attachments btw.