While I get the inclination to think of this in a dev perspective, I think it's ultimately the players who are more important to consider here as it is to their benefit. Yes, it would be good to have a system that is easy to fill out by devs and doesn't take half an hour per game, but if that leads to a subpar content rating system, it's not that useful to implement.
My own inclination in this case is to have some broader subject matter tags that can be chosen, after which some refinement tags are suggested to help branch out to more specific subjects. It should also be possible to add multiple subset subjects.
Some suggestions for categories and subsets:
- Violence: cartoon/fantasy violence, violence towards children, intimate partner violence, etc.
- Sexual content: heterosexual sex, homosexual sex, intersex sex participant(s), transgender sex participant(s), group sex, masturbation, fetish, etc.
- Alcohol/drug use: marijuana, alcohol, smoking, hard drugs, etc.
- Coarse language: sexual innuendo, sexually explicit language, blasphemy, slurs, etc.
- Mental health/abuse: child abuse, domestic abuse, depression, self harm, etc.
- Common phobias: spiders, insects, needles, etc.
This would allow the developers to fill out the contents in broad strokes if they aren't interested in being super specific or want to avoid spoiling their games, but it also allows them to get more specific for players who asked about specific subject matter or if they want to be specific in the first place. The one flaw I can think of is that some subjects that fall under the broad categories might apply to multiple broad categories (rape would fall under violence, sexual content and abuse, for example), so it would be good to have some subjects automatically apply more broad categories when picked.
I personally think age limits are only useful in a legal sense, as different people mature at different rates. I'm not particularly interested in age ratings as a result. The problem I have with the categories of "mature" and "adult" is that the line between them is very blurry for me personally, especially for games. I would personally only mark with ages or age categories if a product is intended to only be consumed by legal adults (basically: porn).