I will start by saying that after reading this meta post about a declined feature request to allow moderators to grant commenting privileges, I am skeptical that my suggestions/thoughts will get positive feedback, but I will try anyways since I think there are real and unsolved problems regarding this topic.
In the question asked here regarding the necessity of 50 reputation as a bar for allowing comments, the most highly voted answer specified that the main reason is spam protection. This makes sense to me, and I completely understand that giving new users the ability to comment right away (or almost right away) will create a flood of comments with no actual value.
From my very limited stackexchange experience, it seems that in some communities, getting 50+ reputation can actually be very challenging. For example, in math.stackexchange, since mathematics is such a huge area, finding new and trending questions one can answer is actually a difficult task, unless one is truly a math expert (at the very least a graduate mathematics student). In addition, it also seems that contributing to older posts (even ones without an accepted or a complete answer) will usually not earn the user new thumbs: there are many posts that are a couple of years old, and these mostly stay inactive even if new and valuable information is added. This is also true for suggesting edits to older posts. I am sure there are other communities that pose similar challenges for responsible beginners who aren't already experts in the field. I want to emphasize that when I say beginners I don't mean high school students: even excelling undergraduate math students will have no chance to answer the vast majority of new questions.
Therefore, I think that considering new ways to earn the basic privileges of the site (mainly commenting), such as time since registration, number of days performing an activity etc' can be beneficial. This will still prevent new users from creating an account immediately after they found a single relevant question and automatically starting to comment on it and related posts. However, users who are responsible, are truly interested in being long-time stack exchange members and didn't join just to ask a question and disappear, will always eventually be able to be more fully participating members.
I am sure such a feature will also lower the amount of content posted as answers posted simply because the user doesn't have commenting privileges, which to my understanding is a relatively common and unwanted phenomenon, which shouldn't be suggested as a workaround. Commenting can also be more likely to properly revive an old inactive post, since it directly notifies the relevant answerer rather than the asker.
Edit: explaining the difference between my question and this: In my opinion, the association bonus provides a full solution to the problem described in the other question, which was sharing reputation across different stackexchange forums. My problem is not concerned with sharing reputation per se, but with the initial problem of obtaining reputation in a single forum to begin with. For example, many undergraduate students use a single stack exchange forum to help with their studies, and might not have other interests or knowledge relevant to other forums, in which case the association bonus will be of no use. As I stated in the comments, I think the association bonus is still a good partial solution, but it is not a full one. I might accept one of the answers mentioning it since it is significantly better than nothing.