It will depend on the merits of the specific question — because this type of question is not inherently outside our scope — and on whether any recognised theory work on the desired subject actually exists.
Overview questions related to RPGs are…
on topic, certainly. They're about RPGs. Our most prominent open overview questions are
not inherently primarily-opinion based (unless the core of your question is for evaluations of the theories! don't do that here)
sometimes too broad, but sometimes not—this will vary with the specific question.
Go for tightly-defined, clear categories of things and it should be OK. RPG theories is kinda waffly and imprecise enough to be too broad—asking for major, well-known RPG theories is probably precise enough to not be too broad as the set that qualifies then is small and fairly clear-cut. (Examples that don't qualify, if they're mentioned by answers, will be weeded out by the judgement of voters voting on such answers.)
Avoiding a list question is not too hard since an overview is a singular, integrated thing. Historically, we've had no trouble with questions asking for an overview, as they usually get responded to with one very good answers. Any small answer that is just a single thing and a description of it are fundamentally not answering the question; so the question being responded to as if it's canvassing for list items wouldn't be the fault of the question, but of answerers missing the point.
However, no matter how tightly you categorise the overview subject, some subjects in RPG theory simply don't have any widespread agreement or recognition, due to the youth of the field. Such questions will probably be closed as too broad (or opinion-based), because of a wide field of lackluster candidate theories and/or dispute over which, if any, are even worth calling "theory."
not unclear (unless the specified set of interest as mentioned above is poorly-written or -defined)
whether it's a duplicate of any existing question will depend on the subject. We don't have an overview of RPG theory frameworks that I know of, but we do have an (sort of†) overview of player taxonomies.
So, a priori, such questions do not have an inherent problem that voids their acceptability in all cases and all ways. Such questions can easily be put on hold on the merits of the specific question, of course, or because of the non-existence or youth of the desired subject within RPG theory (which is generally unlike even esoteric subjects in religious studies), but questions of this general type are not inherently outside our scope.
† I say sort of, because it's not a singular overview so much as a failed experiment in finding a valid use for listy questions. We don't have a singular overview question of player type/behaviour/style taxonomies, but there's no widely-accepted rigorous discussion of such that would qualify as theory anyway.
