The “bulk invite” tool has a few hidden super-powers, including the ability to add groups to invitees and set a target topic. This is all explained on the howto document, but I know I didn’t discover this at first. Would it be worthwhile adding a small button next to the “bulk invite” button which links to that topic?
I thought about suggesting a modal popup with instructions directly inline, and the file upload button there, but I think that’d require a decent design, and would be the opportunity to do other awesome things like preview, paste directly, etc. – all of which I think should be out-of-scope for now.