Hot damn, that is a good point!
As I remarked in edits to my major post on the Answer to the Ultimate Riddle a while ago, the answer to the Ultimate Riddle is written on the back of AURYN, the wish-granting amulet from the Neverending Story whose shape appears in the cherubs’ combined lollipop. From wikipedia on it:
Two mythological serpents, symmetrical, bite at the other’s tail. In the book, they form an oval, and are not intertwined. One serpent is white and one is black. Each has an eye to correspond to the color of the book’s print, red and green. It may be noted that the film version has the two snakes in an “Infinity Knot”, a kind of grief knot which looks like a more intricate variation of the figure “8” infinity symbol and another sign of ouroboros. The two snakes represent the dual nature of the two worlds, Fantasia (German: Phantásien) and Reality, but also the twin nature of their mutual creation and destruction. On the back of AURYN are these words:
“Do What You Will” (German: “Tu, was du willst”).
And that link it gives on ‘true will’ is similarly enlightening, sounding quite a lot like the role of hero titles in Homestuck:
According to Crowley, every individual has a True Will, to be distinguished from the ordinary wants and desires of the ego. The True Will is essentially one’s “calling” or “purpose” in life. Some later magicians have taken this to include the goal of attaining self-realization by one’s own efforts, without the aid of God or other divine authority. This brings them close to the position that Crowley held just prior to 1904. Others follow later works such as Liber II, saying that one’s own will in pure form is nothing other than the divine will. Do what thou wilt shall be the whole of the Law for Crowley refers not to hedonism, fulfilling everyday desires, but to acting in response to that calling. The Thelemite is a mystic. According to Lon Milo Duquette, a Thelemite is anyone who bases their actions on striving to discover and accomplish their true will, when a person does their True Will, it is like an orbit, their niche in the universal order, and the universe assists them. In order for the individual to be able to follow their True Will, the everyday self’s socially-instilled inhibitions may have to be overcome via deconditioning.
Such as, if one’s true calling were that of a “Seer of Light”, for example, tasked with guiding others with one’s understanding of importance and fortune? :)
Now, granted, that wikipedia page on AURYN has changed quite a few times. However, even if you look at the version of the page as it appeared right before Homestuck started, or even before Problem Sleuth started, the wording is similar:
On the back of AURYN are these words:
“Do what you Wish” (German: “Tu, was du willst”).
And it still linked to the concept of True Will, et cetera.
Of course, Andrew probably read The Neverending Story quite a while ago, not just cliffnotes as a refresher, considering he felt the urge to reference it heavily (and AURYN) even with his Wizardy Herbert drafts (the important “mobius slipknot” artifact therein).
So, Andrew could very well have been hiding a reference to the answer to the Ultimate Riddle in every intro page in Homestuck…
Except, to be fair, the phrase also started Problem Sleuth. So probably not. But you know how he is with things becoming retroactively important, after all.
The choice was a natural one: natural for the reader submission and command format, and natural for its Problem Sleuth consistency. But that doesn’t rule out the possibility that he had another reason in mind as well, especially considering how he started the story with the Ultimate Riddle in mind as a major theme, if not the (heh) ultimate one.