This is being worked on for the future 4.2.x branch (ETA: still a very long time).
This effectively adds back the ability to have regular forum attachments on wiki pages.
Inspired by our recent work implementing custom fields, we figured out a way to avoid the whole 1-user problem by adding a couple of layers between the attachments and the pages themselves. Basically, XenForo thinks the attachments are directly on the page, but the page doesn't know that. Each edit of a page references an attachment "set", and each set associates the currently attached attachment IDs. This avoids the problem VW3 had of accidentally deleting attachments if the page was later edited by a different user than the uploader.
In this way, adding or removing an attachment from a page only creates a new edit. And the attachments are still there in case you need to rollback (in VW3 attachments would be gone forever if they were removed and could not be rolled back). A caveat to this is that a user desiring to "remove all my uploads" will be out of luck since the attachments will still be there unless they can delete every edit that had that attachment (in VW3 a user could do this and potentially wreck the content).
A user who doesn't have permission to change the attachments can still edit the page (without accidentally deleting all the attachments because the attachment editor is missing -- a problem VW3 had).
You can quickly see what attachments have changed in the page's history.
There are options to render attachments: at the bottom of the page (like every other forum post), as a separate "Attachments" tab, or as a sidebar widget.
Drag&drop support currently works well.
There is still plenty of work to go on this feature to flesh it out (as with the rest of 4.2), but I am actually really excited about this one.