More of a legal answer than necessarily a historical answer, but, at least in American Supreme Court jurisprudence of the 20th century with which I'm familiar, these kinds of comments are fairly common really and sometimes eventually effective. See, e.g., Justice Harlan Stone's fourth footnote in his 1938 decision of United States v. Carolene Products Company, which suggested a more stringent standard than the rational basis test for future, hypothetical situations and which eventually led to the establishment of the concept of levels of judicial scrutiny and of strict scrutiny. This was ultimately a foundational development to modern constitutional jurisprudence. Thomas actually references this foot note specifically in his recent dissent in Whole Women's Health v. Hellerstedt. You can read Stone's decision here: https://supreme.justia.com/cases/federal/us/304/144/

What these kinds of comments and occasional legal suggestions or hypotheticals are is something called "obiter dictum" (sometimes just "dicta") in fancy law Latin, but it essentially just means any commentary in the decision of a case that is not necessary to reach the actual legal resolution of the controversies at issue in the case. Dicta is not binding, even if contained in a binding decision of the Court. It is noteworthy that the determination of what exactly is dicta and what is actually the holding of any given decision can be fraught with argument and the exact definitions of each of these terms is still being explored. See e.g.: https://scholarship.law.gwu.edu/cgi/viewcontent.cgi?article=2498&context=faculty_publications

However, statements like Thomas's or Stone's call for reevaluation of any legal standard under some hypothetical future challenge or whatever have you would be easily classified as pure dicta because those considerations are wholly external to deciding the actual controversy before them in the given case. When used by a justice of the Supreme Court these comments can be and often are legitimately made with the intent to shape the trajectory of legal development going forward however those justices see fit. The real potential weight of this kind of dicta to actually cause change can probably be measured by the number of justices joining in the opinion containing that dicta. So a single justice writing a lone dissent probably won't drive legislative developments or novel legal challenges in the same way that a statement in a majority opinion might.

Ultimately, the inclusion of dicta and even dicta advocating for a specific future legal development or change is not a distressing departure from any judicial norms in concept. However, it is important to note that the specific legal changes suggested in dicta might themselves be extreme or distressing fringe legal theories that probably should color your perception of a given Justice's biases or understanding of the law.

Although the other answers are accurate, they are not addressing the specific context of the comments you asked about. First, some background. For much of the Supreme Court's history, parties could appeal to the court as a matter of right, as long as the court had jurisdiction. Congress created the United States courts of appeals with the Judiciary Act of 1891, and from then on federal cases were appealed as of right to those new, intermediate courts of appeals, and further review in the Supreme Court was discretionary. That is, the court could grant or deny review (called certiorari or cert.) for any reason it thought appropriate. The basic idea was that there were too many appeals for the court to handle, so this lowered the court's case load. But certain appeals from state courts could still be brought as of right until the Supreme Court Case Selections Act of 1988. Since then, nearly all of the cases the court takes up are discretionary.

So, there is an additional step in the process that normally doesn't get much public scrutiny, which is deciding which discretionary appeals to take. The court has traditionally granted certiorari if 4 justices vote to take it up, although that is by practice rather than rule or statute. The court explains part of what goes into its considerations in Supreme Court Rule 10:

Review on a writ of certiorari is not a matter of right, but of judicial discretion. A petition for a writ of certiorari will be granted only for compelling reasons. The following, although neither controlling nor fully measuring the Court's discretion, indicate the character of the reasons the Court considers:

(a) a United States court of appeals has entered a decision in conflict with the decision of another United States court of appeals on the same important matter; has decided an important federal question in a way that conflicts with a decision by a state court of last resort; or has so far departed from the accepted and usual course of judicial proceedings, or sanctioned such a departure by a lower court, as to call for an exercise of this Court's supervisory power;

(b) a state court of last resort has decided an important federal question in a way that conflicts with the decision of another state court of last resort or of a United States court of appeals;

(c) a state court or a United States court of appeals has decided an important question of federal law that has not been, but should be, settled by this Court, or has decided an important federal question in a way that conflicts with relevant decisions of this Court.

A petition for a writ of certiorari is rarely granted when the asserted error consists of erroneous factual findings or the misapplication of a properly stated rule of law.

The vast majority of cases get certiorari denied without comment in an order list that's just a table of case names and numbers.

Unsurprisingly, there are disagreements about when to take cases up, and those sometimes play out in dissents or statements about the denial of certiorari. A dissent says that the author (and any justices joining the opinion) voted to grant certiorari and usually explains why they thought the case was important enough to warrant review. That often means that the justice discusses what he or she sees as flaws in existing case law. That is exactly what happened here. The court denied certiorari, and Justice Thomas issued a dissent explaining why he thought the actual malice standard is of questionable constitutional support and should be revisited.

Other times, justices offer a "statement concerning the denial of certiorari," which is more varied. It can explain the shortcomings the justice saw in this case that led to the denial. It can explain what would make a good case to raise the issue. Or it can explain how they think the lower court erred but that it's not a good candidate for review because the Supreme Court does not engage in mere error correction.

Neither dissents nor statements from the denial of certiorari are at all new or particularly uncommon, but they were unnecessary for a big chunk of the court's history because, as explained above, the discretionary review that leads to them did not always exist. How frequently they're issued varies quite a bit from term to term, but there have been a few to a few dozen every year for the past several decades at least.