Often, people post follow-up comments to fix problems with previous comments (such as here), and often, in doing so, they wish for an edit feature.
In order to have a comment feature that only allowed editing of your own comments (and surely, you wouldn’t want one that allowed anyone to edit anyone’s right…?), I’d have to set up a login of some kind, whether Google, or otherwise. I’ve never done that, and have always maintained a pretty open and freewheeling comments section here, and overall, it’s worked all right. I know that I don’t like to have to log in (or worse, set up an entire account) to comment elsewhere, and when I have to do so, it usually results in my not bothering.
So be careful what you wish for.
[Update late morning]
OK, it’s not exactly an edit feature, but I’ve added live preview.