It would be neat to have in Special:CentralAuth a count of the number of uploaded files per wiki.
This sounds more like a want to have than a need to have. Would there be any real benefit for this? We could also include a log count, but I'm not sure that it would add much valuable and useful information.
Per T136533, I'd say this isn't really beneficial - the editcount says enough about the involvement in most cases, and adding extra data might make it less clear. Specifically file uploads are not really meaningful information, and my guess would be that it will add mostly columns with a lot of zeros and maybe a number on commons. I don't believe this is information that's necessary to be seen in the blink of an eye, and as file uploads are also counted as edits, looking a bit further might provide answer to what you are looking for.
It might be a good optional addition to the existing labs tool; https://tools.wmflabs.org/quentinv57-tools/tools/sulinfo.php