I thinks sites like Exhentai are already highlghting other stuff other than simply the uploader name, like adding tags are who does what translations.
I meab, we have the user reports on Isshikei that are already doing this, and that was also my goal when initially suggesting this, but these reports are fairly hidden under a link under "More" now.
A hard cap is still the worst solution of all of this. Like, you have found a big batch on Pixiv (that happens sometimes) and then you can't even upload all of them, despite being so-called "unrestricted". That sounds like it will create tons of frustration, actually. If that's done then the cap should be pretty high, like around 200 uploads and shouldn't cap at 50, since it would also slow down Danbooru and would lose content with that. Admittingly, that's the worst case, but it should get avoided.
I personally am for number 3, like I said above.
Highlighting other stats shouldn't be that difficult. The data is already gathered, there should only be a way to make it better accessible and visible.
But on the other side, number 3 doesn'T seem to have anything to do with "prolofic" uploaders. If the problem is really that only a few users are uploading the "best" stuff then it doesn't get solved. The apparant focus of uploading will simply be shifted to more communical work since other stuff gets attention, but the same users will keep on uploading.
While I highly support this, it has nothing really to do with getting other users to upload or pulling some users back. It is nice, but is an independant act, actually.
The only thing that would actively attack "prolific" uploaders is hiding the uploader's name, but I see some problems with that: If the uploader's name is hidden, then the original uploader loses the responsibility to tag their uploads.
Now, let me explain what I mean: Having no name means that you can't "snipe" each other anymore. Therefore, both users will start tagging one post and I can ensure you that there are different ways to apply tags to posts since not all definitions are hard, like breasts size or hair color. I fear that this could lead to tagging wars and it already has lead to tagging wars in the past, even with the uploader's name present.
Especially during Pixiv rush (midnight in Japan) when a lot of images are shared in a short time, I could imagine quite well this scenario and users not going bananas over uploading but instead over tagging.
Another issue I see with making the uploader's name nameless is really the cut of responsibility. Tagging your uploads is mandatory, so it would make that tagging is actually reserved to people that do actually care that an image is well tagged and that are not that many, actually. It's especially hard to keep track of it, since there are so many posts changes and uploads each day.
There are some search queries that will show you low tagged posts, but then these posts getting tagged with tagme, and that not too short. Meaning that a lot of posts will be tagged like that and you can't really get behind the workload if you try to responsibly tag every image under this tag. Tagme is already treated by a handful of people already...
Regarding well-tagged uploads, I fear that exactly this will happen. I don'T say that it's 100% sure, but some users are already only tagging the bare minimum despite knowing more tags and I fear with less influence to push users to tag "their" stuff from a handful usersthe community, more posts will be tagged low.
For posts that are posted during rush, too many people will tag an image when it should only be one and creating tagging war and other stuff that aren't multiple persons are going for are probably ending up with mediocres or less tagging.
The other problem would be posts like post #2974764. Third-party edits. Since these uploaders can't be monitored that well anymore, this stuff might get uploaded en masse then. Now you could say that we can look at the tagging history of the posts that reveals the tagger, but then you could just have the uploaders name. It's far less complicated. On top of that, only Mods can see that. To contact every time a Moderator to tell this user to stop uploading this crap is rather irksome.
You could do it like that: Hide the uploaders name, but only up to Builder level users. There are plenty of Builders on the site and they could still take care of this pretty easily. Of course then you have to ask why we should hide it at all, because I think don't think it will be a motivation for Members to start becoming Builder simply to see who uploaded what.
Yes, hiding the uploader's name will solve that dilemma that only one user is uploading from Touhou, but there are some unwelcomed side-effects as well and it's easier to abuse uploading per se then.