Not an inherently bad idea I feel (I remember using it a lot back when MAL had that function), but hopefully there'd be a way to ensure that this type of thing doesn't devolve into a messy flame war thing, like when MAL had it.
I heard it was on MAL, what exactly happened?
They eventually took it down after making moves to be more of a legitimate platform for anime & manga, but people could leave comments on an anime's page for subgroups that did the show, and those comments usually devolved into flamewars and slurs being thrown around. I'd say maybe 5% of the time you'd see a useful comment about the quality of a subgroup's subs, if that much.
I figured it had to do something with legitimacy, which was why I said I wasn't sure if it was something that would ever be implemented here.
I think if Anilist doesn't plan to partner with Anime companies such as Crunchyroll or Funimation, it should be a safe move. Although I don't know all the legal specifications.
That aside, it is something I would love to see if it is something they can do and don't have an issue with!