They have done a few things over the years, normally things that did not make it outside Japan.
Some of it I imagine is in rights hell (how much of this sort of thing is based on a manga that might since have been sold, this in addition to the usual who owns what in game world with the added bonus of is being 20 years later). They also have the problem of submitting to the various censorship bureaus and expected return for it (it is seldom a cheap hobby to get the stamp of approval, if your additions to a game include a small blurb, 3d filter and maybe a changed control icon then yeah). Being Nintendo they also have the "we want all the control" aspects and probably don't want to be releasing unproven (I mean it was not worthy of release originally...) content lightly.
As far as centralised sources. I doubt many places with an archival, proper info scraping (if they did not think to include a full file listing* from the archive then they are seriously lacking, and I would also say if you seriously used the datamining to mean something no commercial data miner would ever be tasked to do something similar for then you are also behind the curve) or hacking mindset will be willing to go on record as playing with files this hot and not necessarily with a "in the public interest" backing. To that end this might be a "be the change you want to see" type deal, that or you continue to piece together things from specific interest groups as they look at their chosen field.
*were I to play archival hacker info scraping data science boy reporter then what I have already seen discussed and conventional approaches would be spun into
Full file listings, sizes and dates as a matter of course.
Beyond that there are several broad categories of info people will care about
Straight unreleased games, be it at all or translated but not released in a given region (this can include separate English translations for Europe and the US, and things released later as emulated games or ports on later systems).
It was noted that various internal archives of all known or known to a region games were present. Compare and contrast between known archives like those of https://no-intro.org/
. Some such archivers have claimed to find unknown revisions mentioned, and have also claimed that the dumps out in the world are superior quality (Nintendo's archives having errors), this all in addition to gaining some idea of how Nintendo et al stores things internally (this is not ines header country it seems).
Betas of games.
Source code for games. Comments naturally being one of the main targets but you might also quash some rumours and myths. This can also include high res versions of textures, audio and the like. Source code to betas might also be of interest for things mentioned shortly. Some also are full repositories so might even have diffs available.
Tools to build source code for games both to build source code and to get an idea of what devs of the day had available to them and what could reasonably have been done. For later systems you might also find tools to handle file formats. You might also find things of interest in the source code for games and betas if debug hooks are left in (certainly I have pulled out tools, scripts and notes from various isos and unpacked ROMs over the years, and it would not be the first time either https://www.pagetable.com/?p=28
Development notes, project plans and beta test results for games. Anything here really but changes made (content and featured removed and added), bugs squashed and the like. This might be PDF so harder to scan with basic text grabbing options.
Localisation notes if censorship is undertaken, or maybe just in general.
Information on internal hardware, custom chips and board designs. Possibly for general interest and seeding a more advanced repair culture ( https://circuit-board.de/forum/index.php/Thread/13913-STRIP-CLUB-PCB-Scans/?pageNo=1
giving us https://www.dropbox.com/sh/33886pwfi08kvxg/AAABOeOZqH1v53pUM_-8uHrOa?dl=0is
nice and all but compared to what I see available for https://www.youtube.com/channel/UCl2mFZoRqjw_ELax4Yisf6w
to play with when repairing apple hardware then... yeah).
Some mentioned CAD so it might be nice to have CAD documents on plastic shells. Most have probably already been made with basic measuring tools but tolerances if nothing else would be nice to have.
CAD might also feature cancelled hardware and peripherals.
BIOS/firmware files, especially for random regions and peripherals.
Repair tools that might be available -- repair stuff often bypasses various protections too which can lead to new hacks.
Any cryptographic keys. Private is cool but public might yield something as yet unknown for some oddities.