TL;DR. Stack Exchange does not have any functionality to "retire" on-topic questions. The "Historical significance" lock reason is for very specific use cases where the question itself is now off-topic, and intrinsically so. The use of this lock reason to simply "retire" a question would be, IMHO, abusing that functionality. As is generally the case, continued community moderation of the question is the appropriate way forward.
Quite frankly, I don't see under what guise we can lock the question while at the same time adhering to the proper use of this tool. Of the reasons for locking questions we currently have, the closest match (here meaning not obviously inappropriate) is the Historical significance reason, which is described as follows in the post notice.
This question exists because it has historical significance, but it is not considered a good, on-topic question for this site, so please do not use it as evidence that you can ask similar questions here. This question and its answers are frozen and cannot be changed. More info: help center.
That is, the intended use case for this is when a question is (no longer) on-topic, but is nevertheless useful to the site. And recall what happens when a question is locked for this reason (from Meta Stack Exchange).
In addition to the post notice being prominently displayed, posts which are historically locked are "frozen in time": they cannot be voted on, flagged, answered, edited or commented. Historically-locked questions are omitted from normal question lists (those on the home page, /questions, and the various per-tag lists), but can still be found by searching for words in the post or title (via either site-search or Google, etc). The visual appearance of the entire post is altered by removal of the voting arrows from the question and all answers.
So locking the question for "historical significance" will completely freeze the question (and its answers) in their current state. Forever. (Or until another moderator unlocks it, or uses special powers.) To give an example, here is a question currently locked for historical significance: Can I use my powers for good?
Other sites seem to be able to deal with questions with a high number of (deleted) answers without resorting to locks. Consider the following question on Stack Overflow:
Currently that question has 62 undeleted answers (and I am told 19 deleted answers). The undeleted answers include numerous flat out incorrect answers, and a number of duplicate answers (even a self-duplicate: someone posted essentially the same answer twice). The latest (undeleted) answer was posted on 10 Nov 2016, and the SO community seems to be moderating it just fine. (The deleted answers include your usual comments-as-answers, and several approaches using languages other than Java, the language specified in the question's tags.)
And this is just an example. There are other questions on Stack Overflow with many more deleted answers: 38, 41, 62.
Thanks to Daniel Fischer for supplying the information about the deleted answers to these Stack Overflow questions.