Depends what ratings are intended to do - if they are just to be informative for potential viewers then the kind of system you propose sounds good.
But, if the main purpose is to legally restrict access based on age, such ratings wouldn't really do the job.
Plus, of course, there's quite a range within each category - language could mean something as innocuous as "bum", or something as deeply offensive as "Belgium" or "Barbara Streisand".
I suppose you could have age ratings for each subcategory - L18, V12, N0, S0, D15, but it'd start to get complicated pretty fast. Plus, presumably, whatever the highest of those ratings was would still be the overall rating. At which point we're back where we started.





There's a characteristically interesting look at this by David Allen Green, including:
His view is that they must think there's a reasonable chance of it coming to pass or they wouldn't be taking the financial hit.
Of course, it's great publicity for them and her, so maybe it balances out in the end.