Most questions tagged as "reference-request" seem to be people looking for specific papers, or for proofs of specific facts. I would guess that a "roadmap-request" is a request for, well, a road map - which sequence of books or papers one can use to learn some new topic. Of course there's no reason why this isn't a reference request, but in practice there are two very different types of reference requests and it might help to give them different names.
Of course, there's the problem that people won't know what the different tags "mean" if they have meanings that are only apparent to people who read meta.
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