The point of a "ratings board" is to have authority over the rating that is given and have a context for the ratings where they apply.

You can't do that worldwide. You just can't. Never ever. 

You will always find things that are considered vastly differently in different places. Just a random example, smoking. There are places where they have to digitally blur out or remove cigarette smoking from media, or risk higher ratings or even a ban. And we do not even touch the subject of anything remotely sexual or violent yet. There is not only an adult yes/no situation for ratings. You have to decide if it is ok for 6yo or 12yo or whatever ages you will have categories for.

There is not even worldwide consensus on those age categories. Some have 17, other 16, other 15, than there is a PG concept (ok if watched with parents) and some places have a category for 19, 20 and even 21. Also some content might be illegal in a place, so rating it is pointless there.

So in a context, a ratings board and only the ratings board has the authority to declare a media to be in a certain category. Their rating category. And some of those are legally binding. A publisher can't just say, the content is T according to ESRB, because only ESRB has authority to do so.

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I suggest you speak to some developers that have published on Steam and steal the idea behind their extensive questioning or whatever they use. I dimly remember reading that you have to click several checkboxes or whatever to describe your content. So they probably have a huge sheet of topics you need to answer yes/no or give a weight how often things happen. Like smoking, swear words, nudity, violence, blood, and so on.

And then they can apply the known rules of a certain location to guess a typical rating for that area. Because as you know, getting an official rating for an indie game is not that easy. And no one bothers to do so, if it can be avoided, because those rating boards want money. A lot of it. We are talking about 1000 to 3000 $.

What this future rating board could do, have such a questionaire but make sure it is filled out honestly - or have it be filled out by users/publishers/board members. And then calculate predicted ratings for different regions. 

Itch's age categorys are adult (actually the vague safe for workspace plus minors) yes and no and the publisher has a questionaire of one question accordingly. It is usually answered either honestly or conservatively on the side of unsafe. But even with that one question, there is bias, because the things in the popular horror section would have an 18+ rating in many places.

A platform could show either the questionaire directly or the different predicted ratings or a combination of those. So users might be able to filter out games with certain topics or at least see a detailed or summarized justification for a rating. Some topics would encompass others, like, if you have drugs, mentioning smoking is not needed or things like that. Mentioning blood, if you have gore is also pointless.

This isn't something that would work at all. Not only are ratings subjective, someone would have to play through every single game listed and rate each one in a logical manner, which would cause another massive issue, like having every single game taken down until Hell (or Naraka, or the Abyss, or whatever underworld you prefer) freezes over, that way they can all be rated. Then, we might as well be waiting for the Apocalypse, because they have to be put back up again, after all.

You've also got to take non-game media that's hosted here into consideration as well. Who's going to rate all of that? How much longer will it make the backlog for things that need to be rated?

And then, if you get the ERSB involved, who the hell is going to pay $1500 per item to get it rated? Especially considering that all media on the site would have to be rated-- and you cannot ask people who make free things to pony up $1500+ to get their things rated so they can be hosted here.

So yeah, no, something like this just ain't gonna fly.