Earlier quoted context omitted.
Regulating the format and presentation of displayed information, on some kind of online publication, is almost certainly regulation of speech. 1A violation.
It's as much of a 1A violation as regulating that you can't preach the gospel with a megaphone in the middle of Times Square.
That said, such a regulation would actually be unconstitutional unless it’s narrowly aimed at real concerns like blocking traffic. Snyder v. Phelps established that you can go protest with signs saying “God Hates F*gs” and yell at people during a military funeral. Believe it or not, sometimes free speech may be distasteful and disruptive.
The virtual world is very different. The audience is willing, there’s no passerby, no blocking traffic. Competing rights go out the window.