We record some data about actions taken by the user in EventLogging (primarily, we record an event every time the user views a step of the upload process). We should probably look at it again; the last time anyone did was in 2014. In particular, I'd like to know how many of the users beginning an upload process (entering the "funnel") end up completing their uploads.
I'm writing some queries and will post results here. Perhaps we should email them to the Multimedia list or put them on mw.org later.