TL;DR
On the Internet the word comment has been widely adopted for a specific use, i.e., (a place to) dump your opinion on someting. SE comments are better than this. Rename them to remarks to avoid the confusion.
What the dictionary says
From Merriam–Webster (boldface mine):
Full Definition of comment [noun]
: commentary
: a note explaining, illustrating, or criticizing the meaning of a writing
a : an observation or remark expressing an opinion or attitude
b : a judgment expressed indirectly
Full Definition of remark [noun]
: the act of remarking : notice
: an expression of opinion or judgment
: mention of that which deserves attention or notice
Full Definition of remark [verb]
transitive verb
: to take notice of : observe
: to express as an observation or comment : say
intransitive verb
: to notice something and comment thereon —used with on or upon
So, as far as the dictionary goes, the distinction between comment and remark – as far as it applies to Stack Exchange – is a subtle one at best.
What the dictionary doesn’t say
What the dictionaries fail to capture (because it’s only slowly affecting how we perceive the language) is that the word comment has been used by various Internet platforms for a feature that allows every user to express their opinion or whatever they like on whatever was posted – mostly unmoderated. This leads to most comment sections on the Internet being a read-only dump for the unfiltered mental outpour of attention addicts. Youtube comments have already become a stock comparison, signifying the bottom of the Internet. (Just in case you are not familiar with them, the introduction of this Wikipedia article manages to illustrate the nature of Youtube comments very well.)
Stack Exchange comments are better than this, yet it is inevitable that a considerable number of users expect them to be like comments elsewhere on the Internet which results in confusion. An extreme example is this comment (in a Meta discussion on deleting comments):
This is a very unclear policy and if that is the case then comments should be renamed to "clarifications to question..." come on the point of comments is to make a comment. When I see a button to add a comment it means I want to comment. You will need to change the user interface if comment isn't and doesn't really mean comments. You'll have to go to each and every answer across all the SE sites to impose such a horrible idea.
Some considerations
Apart from the work to implement this, the only downside of this that I can think of is the possible confusion of new users when they see old posts referring to comments. However, as comments are rarely referred to an the main sites (and should be ephemeral anyway), this should mainly affect Meta, where most users either are aware of this anyway and can be informed via tag-wiki excerpts and similar. Moreover, SE survived renaming offensive to rude/abusive and Not Programming-Related SE survived even two renamings, so I am quite confident that this will be a minor issue.
Ideally this happens simultaneously with a UI change such as the ones discussed here.
If somebody has a better suggestion than remark (that is still generally understood, not too fancy or too restrictive), …
