We'd find it useful to be able to add files to existing items using the desktop uploader, rather than the uploader creating a new item for each upload.
I'd also like to support the idea of all members of a Project having the ability to edit the metadata on each other’s unpublished items. I think you've had this request already.
Both of these would help us when working with large, complex datasets with more than one author.
The second one is already being looked at, you are right. The first one i am not sure on, I'll investigate with the team at an appropriate juncture and return.
I also vote for the 2nd item - the ability to edit the metadata on each other's unpublished items. I'd also go a step further and ask that "super collaborators" on a project be allowed to remove items uploaded by someone else in a project, e.g. replace an item with a new version. This would probably require a 3rd role for projects.