> No, I don't want to go around dividing those things into “accessibility” and “merely aesthetic” buckets, and then only allow the things in the first bucket. For one thing, some of them are both.
I agree, and want to allow everything. Actually, I think perhaps all of them are both, and anyways the end user should control and configure all of them.
> If you are speaking as a web designer, then you don’t get to complain about rounded corners on the viewport.
I think the web designer may have a reasonable complaint about the browser doing that by default with no option to disable it, since that makes it difficult for everyone. However, the user has a better and even more valid complaint about this, especially if it cannot be turned off. However, if the end user adds the rounded corners deliberately then it is not for the web designer to complain about the user's preferences.