The more general question, about whether we allow asking about developer statements which may or may not exist, appears to be yes. That's based on precedents and on it not transgressing any rules.
I think it's also fine to leave it as “yes” after meta discussion, since I don't believe it causes any structural problems that the site isn't equipped for.
Why: these can often be “long tail” questions, which SE handles well
To that point: one of the ways that the site handles questions gracefully is allowing questions to be “forever” both forwards and backwards, and the site rules are built to accommodate that. In the usual case, this manifests in our understanding that there are no questions “too old” to submit new answers to: questions are always open for new answers if they are still on-topic. Even if it's not obvious how new answers could be useful, people are allowed to make the attempt.
The rarer case is the “long tail” question, of which this might be one. “Long tail” questions are those that we don't know whether they have an answer. Whether they do or not can only be discovered by leaving them open forever, so that in the long, shrinking tail of their diminishing views accumulation, the right someone might discover it and have the answer it's been waiting for. There may never be an answer, or it might be answered soon (just, maybe, not as soon as the average we're used to). Either way, we allow and accept that answers may stay unanswered for a potentially long time, so that we can eventually collect the answer, if it has one, and add it to our hoard of curated solutions.
So I think that feature answers how we should handle questions about the existence of developer-statement that may or may not have ever (or be ever) made by the developers: leave them open, protect them from (off topic) speculative answers that add noise to the page and remove the question from the Unanswered Questions list, so as to leave it dangling out there until it catches the eye of exactly the one expert who can help, if they do or will exist.
Of course, this requires a certain degree of patience among the community that we're sometimes unused to, especially in a tag like dnd-5e where we're used to questions getting answers super quick.